for each file field, create a hidden form element to hold the file name that is in the database.
In digital file pro, bind the Default File to the hidden form element.
In the update record server behavior, bind the files name columns to the Uploaded Files A(File Field Name) -> Server file name.
This is covered in the "Applying File Upload to DataAssist Insert and Update pages" tutorial on the Universal Email support page:
universal-email/