Use superglue to glue two magnets per keyboard housing into the holes provided. These magnets will later be used to attach the wrist rests. Align the magnets in both keyboard housings in the same way. For example, the north pole should always face outwards.
If you hold the remaining magnet stack against the case from the outside and use it to pull the magnet to be glued into the hole, you can be sure that it will maintain the specified orientation and not slip. The magnets are very strong and to avoid scratch marks, it is best to place a piece of paper between the magnet stack and the case.
This is how it should look in the end:
Proceed in the same way with the other half of the keyboard.