Hi there. As the title states, the back door handle has fallen off. I can see that there's a threaded bolt on the stump that holds the handle itself, but can't for the life of me see how to het the bolt attached to the handle once again.
It looks as if the securing screw is accessed from the inside of the fluted mounting in the bottom picture; I'd remove the entire unit to investigate further; are the threads in the handle stripped? Good luck.