They should have never had you using QMK to begin with. It really dosent make sense to me why they had you put it in boot loader mood and install 3rd party software. CORE flashes fresh firmware as long as the board is detected. If it is detected its a good sign your using glorious if its not you could still be stuck in QMK.
If it does not show up id say you have 3 options.
- Retry flashing it with using the files the support team gave you
- Flash it with QMK officially and use that insead (it should work with the keymap gui VIA)
- Try and get a replacement PCB