The V5F mudguard comes with two screws in a plastic bag.
On the underside of the rear handle cover, right by where the wheel well begins, you will see two screws. Remove them.
Insert the two longer screws that came with the mudguard into the holes in the mudguard, with the screws pointing upwards (insert them from the bottom, not the top).
Screw the mudguard in where the factory screws used to be, and it should slot into place as it is screwed in.