start by removing the grab handles, then the screws fixing the cover to the tailgate, four IIRC, then pull sharply to release the poppers from frame and the cover is free. Undo the electrical connectors (you may wish to check the wiring, one of mine has chaffed through on a sharp edge) then the bolts holding the lock to the tailgate and it will be free to remove.
Spray the WD40 in the apertures and allow to soak and then simulate locking and unlocking with screwdriver shaft or similar several times to get it worked in.
If you plug the connectors in before fitting and ensure it is in the unlocked position you will see the light come on if you have been successful. Refitting is the reverse.