My exterior door handle came detatched on my.

You are going to be removing trim screws and pulling out panel plugs. So go slowly and look for round caps which are trim panel screw covers. Gently start prying the bottom and the plastic plugs will pop out and usually come with the trim panel but sometimes stick in the metal slot of the door frame. Pull them out and place them in panel for re-assembly.
It is a matter of patience and determining what needs to be removed to get the panel to come loose. Sometimes you have to remove parts like door handles or the trim plate for the door handle.