Copy and paste user ID field to checkinId field?

Question:
Can anyone help me understand how to bulk copy and paste client info from one field to another within each clients’ profile?

Product:
I am trying to set up a barcode check-in system in person after users book a service on my website. This is pretty easily done using the Wix Client Checkin app… however, I need a “checkinId” for each client. We already have individual ID’s associated with barcodes, but just need to copy and paste each individual clients ID to their checkinId field. I also need something to update/copy and paste this each time someone new makes an account on the website.

I have been trying to write manual javascript code to do this in bulk, but cannot seem to get anything to work. Does anyone have any ideas or input to try next? Or maybe some tips on how to write this backend code if that’s the correct route?