Related Records on Conversion

Related Records on Conversion

Hello All, 
      I am having some trouble mapping a conversion for related records on a Lead. I have a separate module that holds a Prequalification Letter for a Lead/Contact.

I mapped a custom button to open a Form that promptly merges the inputted data and sends the document to a few recipients in the Lead and Contact Modules.

The Form on submission pushes data back into the CRM that triggers a conversion into Contact and Deal(Potential) records. I now have lost the PQ Letter record that was originally associated with the Lead. 

Is there a way to grab the new Contact ID and associate it with the now orphaned PQ record?