Make sure your board is clean. You can easily remove grease with some washing up liquid, make sure you rinse off all the soap after cleaning
Unscrew the bottom part from the mount
Remove the protective film from the 3m sticker
Place the bottom part with sticker at the required place. Press down firmly to ensure a good bond
Leave the board for about 24 hours to ensure the best bond between board and mount
Insert AirTag into the bottom part with the metallic part to the bottom screw on the top part of the mount. Screw down until you feel a some resistance. You have hit the rubber seal. Continue turning for about another 1/10 turn ensuring a good seal