Loose passenger side rear view mirror

The mirror is intact within the casing. The casing itself is not damaged and the mirror moves well within the casing using the controls by the side of the driver seat. The place where the plastic casing that holds the mirror is connected to the plastic extension from the car is loose. I tried to move it around to see if it snaps back in place, but it doesn't, and I don't know how to open it up to see what is wrong. Is there any easy fix to repair this?