The lock cylinder is held in to the handle by a clip - which is a pain in the ass to get out. The entire handle is slid into place on the lock (right) side and then it bolts into place via a retaining nut on the non lock side (left), if you're looking at the tailgate from the outside.

I replaced mine with a handle from eBay. Aftermarket part which was actually a little bitter than OEM. Also cheaper: 15 vs 80