The interior handle is attached to the lever that opens the door by a long rod. That rod is a secured by a little plastic clasp that sometimes breaks over time.

You must remove the inner door panel and you may have to fish inside the door to get the rod (sometimes it falls over when the clasp breaks) and replace the clasp. The clasp isn't very expensive at all, and the job of replacing it isn't that difficult.

I hope this helps.