I have always been able to avoid writing code till today. Our marketing team created several hundred Pardot Landing pages for our business partners sales reps to enter leads into. 
These leads come into Salesforce and have a text field  populated called Landing_Page_ID__c . The field is basically firstname.lastname  of the partner sales rep.  

I need to be able to populate a lookup on the lead called Territory_Manager__c . (this is the contact record of the partner sales rep who submiited the lead)  I have created a new field on the Conact called LPID_c which matches the text from the Landing_Page_ID__c.

I am going to watch videos and trailheads but I thought I would ask here first since I am on a deadline to fix this.