The frame mounts using the two screws under the dash (you can feel it with your fingers)
At the bottom you either use double sided tape if you don't want to drill hols or just use two self-tapping screws to screw into the trim piece
I suggest you print and fit both elements before drilling anything
Modifying the facia:
I include the .step file with empty facia for you to design your own
Depending on the switch size (back part) be mindful of the space at the bottom – if you put your switches to close to the bottom edge, it will hang on the frame
Hardware:
You can glue this thing together but for servicability I'd recommend screws :)
The brass inserts I used are 4x4x5mm. Pretty shallow, but the important dimention is 5mm diameter
Screws are any that fit your insers (M5x10 are perfect)