I would like to save the data filled in the form as shown in below. How ever i am not understanding how to do. 

I have a quick action on Account object , on click of quick action button customer opens the form  as shown below . 



Here account name gets autopopulated and additional note needs to be filled by user and on hit on save button this needs to get saved in "Customer object" 

1.Account name : its a custom dynamic lookup
where we can search the record . 

code :

<template>
    <lightning-card>
      <header class="slds-modal__header" data-aura-rendered-by="142:2755;a">
        <h2 class="slds-modal__title" data-aura-rendered-by="143:2755;a"><b>Customer</b></h2>
        </header>
        <div class="slds-m-around--xx-large ">
  
    <div class="form-group">
         <c-custom-Lookup-Lwc icon-name="standard:account"
            s-object-api-name="Account"
            label="Account Name "
            onlookupupdate={lookupRecord}
            placeholder="Account here..."></c-custom-Lookup-Lwc>
    </div>  


    <div class="form-group">  
              <lightning-textarea
              max-length="100"
              message-when-value-missing="Please enter the description"
              label="Additional Note"
              required
              value={description}
              onchange={handleChange}
              class="textAreaCSS"></lightning-textarea>
            </div> 

        
      <footer class="slds-modal__footer" data-aura-rendered-by="145:2889;a">
        <div>
          <lightning-button variant="neutral" label="Cancel" onclick={closeAction} ></lightning-button>
          <lightning-button variant="brand" label="Save" onclick={saveAction} ></lightning-button>
        </div>
      </footer>
    
      </div>
    </lightning-card>
  </template>
  =========================================
  import { LightningElement,wire,api,track} from 'lwc';
import { CloseActionScreenEvent } from 'lightning/actions';
export default class CustomerQA extends LightningElement {
    @api records;
    @api error;
    
    lookupRecord(event){
      alert('Selected Record Value on Parent Component is ' +  JSON.stringify(event.detail.selectedRecord));
    }

    closeAction(){
        this.dispatchEvent(new CloseActionScreenEvent());
    }

   saveAction(event){
    }   
}

=======================================================
customlookuplwc.html

<template>
    <div class="slds-form-element" onmouseleave={toggleResult}  data-source="lookupContainer">      
        <div class="slds-combobox_container slds-has-selection">
          <label class="slds-form-element__label" for="combobox-id-1">{label}</label>
          <div class="lookupInputContainer slds-combobox slds-dropdown-trigger slds-dropdown-trigger_click" aria-expanded="false" aria-haspopup="listbox" role="combobox"> 
           <div class="slds-combobox__form-element slds-input-has-icon slds-input-has-icon_left-right" role="none">
              <div class="searchBoxWrapper slds-show">
                <!--Lookup Input Field-->
                <lightning-input                   
                   type="search"
                   data-source="searchInputField"
                   onclick={toggleResult}
                   onchange={handleKeyChange}
                   is-loading={isSearchLoading}
                   value={searchKey}
                   variant="label-hidden"
                   placeholder={placeholder}
               ></lightning-input>  
              </div>
              
            <!--Lookup Selected record pill container start-->  
            <div class="pillDiv slds-hide">        
              <span class="slds-icon_container slds-combobox__input-entity-icon">
                <lightning-icon icon-name={iconName} size="x-small" alternative-text="icon"></lightning-icon>  
              </span>
              <input type="text"
                     id="combobox-id-1"
                     value={selectedRecord.Name}       
                     class="slds-input slds-combobox__input slds-combobox__input-value"
                     readonly
                     />
              <button class="slds-button slds-button_icon slds-input__icon slds-input__icon_right" title="Remove selected option">
              <lightning-icon icon-name="utility:close" size="x-small" alternative-text="close icon" onclick={handleRemove}></lightning-icon> 
             </button>
            </div>  
            </div>
        
            <!-- lookup search result part start-->
            <div style="margin-top:0px" id="listbox-id-5" class="slds-dropdown slds-dropdown_length-with-icon-7 slds-dropdown_fluid" role="listbox">
              <ul class="slds-listbox slds-listbox_vertical" role="presentation">
                <template for:each={lstResult} for:item="obj">
                <li key={obj.Id} role="presentation" class="slds-listbox__item">
                  <div data-recid={obj.Id} onclick={handelSelectedRecord} class="slds-media slds-listbox__option slds-listbox__option_entity slds-listbox__option_has-meta" role="option">
                    <span style="pointer-events: none;" class="slds-media__figure slds-listbox__option-icon" >
                      <span class="slds-icon_container" >
                          <lightning-icon icon-name={iconName} size="small" alternative-text="icon" ></lightning-icon>  
                      </span>
                    </span>
                    <span style="pointer-events: none;" class="slds-media__body" >
                      <span  class="slds-listbox__option-text slds-listbox__option-text_entity">{obj.Name}</span>
                    </span>
                  </div>
                </li>
                </template>
                <!--ERROR msg, if there is no records..-->
                <template if:false={hasRecords}>
                  <li class="slds-listbox__item" style="text-align: center; font-weight: bold;">No Records Found....</li>
                </template>
              </ul>
             
            </div>
          </div>
        </div>
      </div>
  </template>
  =============================================
  customlookuplwc.js:  
  import { LightningElement, api, wire } from 'lwc';
// import apex method from salesforce module 
import fetchLookupData from '@salesforce/apex/CustomLookupLwcController.fetchLookupData';
import fetchDefaultRecord from '@salesforce/apex/CustomLookupLwcController.fetchDefaultRecord';
import { CurrentPageReference } from 'lightning/navigation';
const DELAY = 300; // dealy apex callout timing in miliseconds  

// Start
import { getRecord, getFieldValue } from 'lightning/uiRecordApi';
import NAME_FIELD from '@salesforce/schema/Account.Name';
// end 

export default class CustomLookupLwc extends LightningElement {
    // public properties with initial default values 
    @api label = 'custom lookup label';
    @api placeholder = 'search...Acc...';
    @api iconName = 'standard:account';
    @api sObjectApiName = 'Account';
    @api defaultRecordId = '';
    @api recordId;

    // private properties 
    lstResult = []; // to store list of returned records   
    hasRecords = true;
    searchKey = ''; // to store input field value 
    isSearchLoading = false; // to control loading spinner  
    delayTimeout;
    selectedRecord = {}; // to store selected lookup record in object formate 

   //getting record id from below function 
    @wire(CurrentPageReference)
    getStateParameters(currentPageReference) {
        if (currentPageReference) {
            this.recordId = currentPageReference.state.recordId;
            console.log('this.recordId==35===' + this.recordId);
          }
    }

// initial function to populate default selected lookup record if defaultRecordId provided  
    connectedCallback() {
        try{
            if (this.recordId != '') {
                fetchDefaultRecord({ recordId: this.recordId, 'sObjectApiName': this.sObjectApiName })
                    .then((result) => {
                        console.log('result===== ',result);
                        if (result != null) {
                            this.searchKey = result.Name;
                            console.log('this.searchKey===== ',this.searchKey);
                            this.selectedRecord = result;
                            this.handelSelectRecordHelper(); // helper function to show/hide lookup result container on UI
        
    //creating a custom event to pass the Account name to parent                
        const answerEvent = new CustomEvent("accname", { detail: this.searchKey });
        this.dispatchEvent(answerEvent);         
                       
                        }
                    })
                    .catch((error) => {
                        this.error = error;
                        this.selectedRecord = {};
                        console.error('OUTPUT: ', error);

                    });
            }
        } catch (error) {
            console.error('OUTPUT: ', error);
        }
    }

// wire function property to fetch search record based on user input
    @wire(fetchLookupData, { searchKey: '$searchKey', sObjectApiName: '$sObjectApiName' })
    searchResult(value) {
        const { data, error } = value; // destructure the provisioned value
        this.isSearchLoading = false;
        if (data) {
            this.hasRecords = data.length == 0 ? false : true;
            this.lstResult = JSON.parse(JSON.stringify(data));
        }
        else if (error) {
            console.log('(error---> ' + JSON.stringify(error));
        }
    };

// update searchKey property on input field change  
    handleKeyChange(event) {
        // Debouncing this method: Do not update the reactive property as long as this function is
        // being called within a delay of DELAY. This is to avoid a very large number of Apex method calls.
        this.isSearchLoading = true;
        window.clearTimeout(this.delayTimeout);
        const searchKey = event.target.value;
        this.delayTimeout = setTimeout(() => {
            this.searchKey = searchKey;
        }, DELAY);
    }

// method to toggle lookup result section on UI 
    toggleResult(event) {
        const lookupInputContainer = this.template.querySelector('.lookupInputContainer');
        const clsList = lookupInputContainer.classList;
        const whichEvent = event.target.getAttribute('data-source');
        switch (whichEvent) {
            case 'searchInputField':
                clsList.add('slds-is-open');
                break;
            case 'lookupContainer':
                clsList.remove('slds-is-open');
                break;
        }
    }

    // method to clear selected lookup record  
    handleRemove() {
        console.log('handleRemove');
        this.searchKey = '';
        this.selectedRecord = {};
        this.lookupUpdatehandler(undefined); // update value on parent component as well from helper function 

        // remove selected pill and display input field again 
        const searchBoxWrapper = this.template.querySelector('.searchBoxWrapper');
        searchBoxWrapper.classList.remove('slds-hide');
        searchBoxWrapper.classList.add('slds-show');

        const pillDiv = this.template.querySelector('.pillDiv');
        pillDiv.classList.remove('slds-show');
        pillDiv.classList.add('slds-hide');
    }

    // method to update selected record from search result 
    handelSelectedRecord(event) {
        var objId = event.target.getAttribute('data-recid'); // get selected record Id 
        this.selectedRecord = this.lstResult.find(data => data.Id === objId); // find selected record from list 
        this.lookupUpdatehandler(this.selectedRecord); // update value on parent component as well from helper function 
        this.handelSelectRecordHelper(); // helper function to show/hide lookup result container on UI
    }

    /*COMMON HELPER METHOD STARTED*/

    handelSelectRecordHelper() {
        this.template.querySelector('.lookupInputContainer').classList.remove('slds-is-open');
        const searchBoxWrapper = this.template.querySelector('.searchBoxWrapper');
        searchBoxWrapper.classList.remove('slds-show');
        searchBoxWrapper.classList.add('slds-hide');
        const pillDiv = this.template.querySelector('.pillDiv');
        pillDiv.classList.remove('slds-hide');
        pillDiv.classList.add('slds-show');
    }

    // send selected lookup record to parent component using custom event
    lookupUpdatehandler(value) {
        const oEvent = new CustomEvent('lookupupdate',
            {
                'detail': { selectedRecord: value }
            }
        );
        this.dispatchEvent(oEvent);
    }
}
============
public class CustomLookupLwcController {
    // Method to fetch lookup search result   
     @AuraEnabled(cacheable=true)
     public static list<sObject> fetchLookupData(string searchKey , string sObjectApiName) {    
         List < sObject > returnList = new List < sObject > ();
 
         string sWildCardText = '%' + searchKey + '%';
         string sQuery = 'Select Id,Name From ' + sObjectApiName + ' Where Name Like : sWildCardText order by createdDate DESC LIMIT 5';
         for (sObject obj: database.query(sQuery)) {
             returnList.add(obj);
         }
         return returnList;
     }
     
     // Method to fetch lookup default value 
     @AuraEnabled
     public static sObject fetchDefaultRecord(string recordId , string sObjectApiName) {
         string sRecId = recordId;    
         string sQuery = 'Select Id,Name From ' + sObjectApiName +' Where Id =\''+ sRecId+'\'  LIMIT 1' ;
         for (sObject obj: database.query(sQuery)) {
             return obj;
         }
         return null;
     }
     
 }