The WHR-L01-W01 is intended to be fixed on the Wifx L1 before any installation on the wall.
The first step is to install the support on the back of the Wifx L1.
Use a torx T10 screwdriver to screw the two flat head screws at the back of the Wifx L1.
Be careful to fix correctly the two screws ensuring the support is not moving. Strength of screwing should be correctly adapted to avoid on the contrary any pull-out of the metal inserts from the plastic body.
The WHR-L01-W01 has space for the screw on one side, make sure that the screws are in place when fully tightened and that the head surface matches the support's surface as shown in the picture.