Its best done with two people. First, slide the retainer tab, the flat piece with the hole in it, in place in the trunk lid and hold it there. Then feed the lock assembly thru the trunk lid from the outside. Feed it thru the retainer as well. Next, insert the lock cover and then slide the retainer over the slot in the lock cover. The retainer will hold everything in place.
It can be done with just two hands, but a third helps hold the retainer.