linking my customer contact form to product form

linking my customer contact form to product form

I have two forms, already populated with many data entries.  One form has client contact info (Customer Contact Data) and the other (Lift Data) has details on the product or products they have purchased from us (handicapped accessibility lifts), including serial numbers, install and warranty expiration dates, and date of last service, etc.  Both forms have a field called "Full Name" and I want to be able to connect the records with matching content in the "Full Name" field in both forms together.  I have messed around with trying to add a look-up, but I'm not getting anywhere, it looks the way I want it to (almost) for the blank form, but what about about the existing data?