How to create a text version of the numeric field "Account ID"
The idea behind this tutorial is to create a text version of the Contact Object numeric field "Account ID" and be able to be compared against the Leads Object field "Company" (Text Field) to return duplicate records. With that done, the 3 objects (Accounts, Contacts, and Leads) will have a field in between that can be mapped in the Cross Object feature to return the duplicate records.
Navigate to Salesforce Setup -> Object Manager -> Contact
Click on the "Fields & Relationships" tab.
On the top right, click the "NEW" button.
Under "Data Type" choose 'Formula' and click 'Next'
In the 'Field Label' write "Text Account Name" Formula Return Type choose: "Text" Click 'Next'
Under 'Formula Options' click the 'Insert Field' button.
Choose: Contact > Account > Account Name, then click the 'Insert' button.
Click Save. Now the "Text Account Name" field in Contact Object is created.
Now you can add this field in your Contact scenario and map it in the Cross Object feature tab.
*Enable the "Cross Object" feature for both "Contacts" and "Leads". Configure the cross object mapping for the Lead Object: Lead to Contact mapping: Company -> Text Account Name