Hi,

Instead of storing the lead result in the query to list store it to Map and query all the address fields like City, Country,State, Pincode .. etc as below .
 

Map<Id,Lead> leadmap= new Map<Id,Lead>([SELECT Id,Name,LastName,FirstName,Email,Date_Of_Birth__c,Service__c ,Gender__c,City,Country,State FROM Lead WHERE Id IN :LeadIds]);

Now while iterating over the leads instead you should iterate over leadmap.values().

so you can get the address field in the Contract directly as below. I have highlited the changes in the class.

 

public class AutoConvertLead {
@InvocableMethod
public static void assignLeads(List<Id> LeadIds) { 
    try{ 
        Map<String,Date> NameDOBMap = new Map<String,Date>();
        List<String> leadNames = new List<String>();
        List<Date> leadDOBs = new List<Date>();
        List<Database.LeadConvert> massLeadConvert = new List<Database.LeadConvert>();
        List<Account> accountsToUpdate = new List<Account>();
        List<Account> accountsToInsert = new List<Account>();
        List<Contract> contractsToInsert = new List<Contract>();
        Map<String,Account> nameDOBToAccountMap = new Map<String,Account>();
        Map<String,Account> newCreatedAccounts = new Map<String,Account>();
        Map<ID,Id> leadProductMap = new Map<Id,Id>();
        
        Id personAccountRecordTypeId = Schema.SObjectType.Account.getRecordTypeInfosByName().get('Person Account').getRecordTypeId();
        LeadStatus cLeadStatus = [SELECT Id,MasterLabel FROM LeadStatus WHERE isConverted = true LIMIT 1];  
        
       // List<Lead> leads = [SELECT Id,Name,LastName,FirstName,Email,Date_Of_Birth__c,Service__c,Ethnicity__c, Race__c,Gender__c FROM Lead WHERE Id IN :LeadIds];
       Map<Id,Lead> leadmap= new Map<Id,Lead>([SELECT Id,Name,LastName,FirstName,Email,Date_Of_Birth__c,Service__c,Ethnicity__c, Race__c,Gender__c,City,Country,State,Street,PostalCode FROM Lead WHERE Id IN :LeadIds]);
       // for(Lead lead: leads) {
        for(Lead lead: leadmap.values()) {
            leadNames.add(String.valueOf(lead.Name));
            leadDOBs.add(lead.Date_Of_Birth__c);
            NameDOBMap.put(lead.Name, lead.Date_Of_Birth__c);
            leadProductMap.put(lead.Id,lead.Service__c);
        }
        
        Map<Id, Account> existingAccounts = new Map<Id, Account>([SELECT Id, PersonBirthdate, Name, PersonGender FROM Account WHERE Name IN :NameDOBMap.KeySet() AND PersonBirthdate IN :NameDOBMap.values()]);
        
        for(account acc: existingAccounts.values()){
            
        }
        //System.debug('Check 1'+existingAccounts);
        for(Account accc: existingAccounts.values()){
            nameDOBToAccountMap.put(accc.Name+accc.PersonBirthdate, accc);
        }
        
       // for(Lead ld : leads){
        for(Lead ld: leadmap.values()) {
            if(!nameDOBToAccountMap.containsKey(ld.Name+ld.Date_Of_Birth__c)){
                Account existingAccount = new Account();
                existingAccount.LastName = ld.LastName;
                existingAccount.FirstName = ld.FirstName;
                existingAccount.PersonEmail = ld.Email;
                existingAccount.PersonGender = ld.Gender__c;
                existingAccount.RecordTypeId =  personAccountRecordTypeId;
                existingAccount.Ethnicity__pc = ld.Ethnicity__c;
                existingAccount.Race__pc = ld.Race__c;
                existingAccount.PersonGender = ld.Gender__c;
                existingAccount.PersonBirthdate = ld.Date_Of_Birth__c;
                accountsToInsert.add(existingAccount);
            }  
        }
        
        if(accountsToInsert.size()>0){
            insert accountsToInsert;
        }
        //system.debug('accountsToInsert'+accountsToInsert);
        
        for(account acc: accountsToInsert){
            newCreatedAccounts.put(acc.FirstName+acc.LastName, acc);
        }
        //system.debug('newCreatedAccounts'+newCreatedAccounts);
        //for(Lead lead : leads){
            for(Lead lead : leadmap.values()){
            //System.debug('Check 2');
            Database.LeadConvert LeadConvert = new Database.LeadConvert();
            LeadConvert.setLeadId(lead.Id);
            LeadConvert.setConvertedStatus(cLeadStatus.MasterLabel);
            LeadConvert.setDoNotCreateOpportunity(false);
            
            if(lead.Name != null && lead.Date_Of_Birth__c != null){                    
                if(nameDOBToAccountMap.containsKey(lead.Name+lead.Date_Of_Birth__c) && nameDOBToAccountMap.get(lead.Name+lead.Date_Of_Birth__c)!=Null){
                    //system.debug('existingAccount==>'+nameDOBToAccountMap.get(lead.Name+lead.Date_Of_Birth__c));
                    Account existingAccount = new Account();
                    existingAccount.Id = nameDOBToAccountMap.get(lead.Name+lead.Date_Of_Birth__c).id;
                    //system.debug('existingAccount'+existingAccount);
                    existingAccount.Ethnicity__pc = lead.Ethnicity__c;
                    existingAccount.Race__pc = lead.Race__c;
                    existingAccount.PersonGender = lead.Gender__c;
                    accountsToUpdate.add(existingAccount);
                    LeadConvert.setAccountId(existingAccount.Id);
                }
                else{
                    //system.debug('lead.Name+lead.Date_Of_Birth__c'+lead.FirstName+lead.LastName);
                    if(newCreatedAccounts.containskey(lead.FirstName+lead.LastName) && newCreatedAccounts.get(lead.FirstName+lead.LastName)!= Null){
                        LeadConvert.setAccountId(newCreatedAccounts.get(lead.FirstName+lead.LastName).Id);
                    }  
                }
                //System.debug('LeadConvert.getAccountId()'+LeadConvert.getAccountId()); 
                massLeadConvert.add(LeadConvert);
                //system.debug('massLeadConvert'+massLeadConvert);
            }
        }
        
        if(!accountsToUpdate.isEmpty()){
            //system.debug('accountsToUpdate'+accountsToUpdate);
            update accountsToUpdate;
            //system.debug('accountsToUpdate'+accountsToUpdate);
            
        }
        
        if(!massLeadConvert.isEmpty()){
            //system.debug('massLeadConvert'+massLeadConvert);
            List<Database.LeadConvertResult> lcr = Database.convertLead(massLeadConvert);
            for(Database.LeadConvertResult leadConvertResult : lcr) {
                //system.debug('leadConvertResult'+leadConvertResult);
                //system.debug('accountid'+existingAccounts.containskey(leadConvertResult.accountid));
                if(leadConvertResult.isSuccess() && !existingAccounts.containskey(leadConvertResult.accountid) ) {
                    Contract contract = new Contract();
                    contract.Status = 'Draft';
                    contract.AccountId = leadConvertResult.getAccountId();
                    contract.StartDate = system.today();
                    contract.ContractTerm = 12;
                    if(leadProductMap.containskey(leadConvertResult.getLeadId()) && leadProductMap.get(leadConvertResult.getLeadId())!=Null){
                        contract.Service__c = leadProductMap.get(leadConvertResult.getLeadId());
                    }
                    if(leadmap.containskey(leadConvertResult.getLeadId())  ) {
                            
                        contract.BillingCity= leadmap.get(leadConvertResult.getLeadId()).City;
                        contract.BillingState= leadmap.get(leadConvertResult.getLeadId()).State;
                        contract.BillingCountry = leadmap.get(leadConvertResult.getLeadId()).Country;
                        Contract.BillingStreet=leadmap.get(leadConvertResult.getLeadId()).Street;
                        Contract.BillingPostalCode=leadmap.get(leadConvertResult.getLeadId()).PostalCode;

                    }
                    contractsToInsert.add(contract);
                }
            }
        }
        
        if(!contractsToInsert.isEmpty()){
            insert contractsToInsert;
        }
    }catch(Exception e){
        //System.debug('Error: '+e.getMessage()+ 'Line Number'+e.getLineNumber());
    }
}
}

Let me know if you face any issues.

If this solution helps, Please mark it as best answer.

Thanks,