PDF Generator Frustrations

I have paid for premium and going through the documentation for the PDF generator and can't figure out how to create a PDF from a specific item in the database. I have used the code for filtering by member ID and that works just fine, but it uses the top item for that member. I would like to do the same filtering but filter by the _id and specify the exact item for the PDF.

I see there is an appendmemberId parameter, is there a way to change this parameter to whatever I want so when the app sends the query param over I can change to filter by id? Or is there a way to do an onClick command for the app button so I could do a wixlocationfrontend.to and send over the getcurrentitem()._id?