good morning and thank you for choosing JustAnswer. The mirror slides down onto the metal tab that is glued to the windshield and locks inbto place. If it is on and just loose then you will need to tap on the top side of the mirror and tap it down into place
NOTE: Make sure the inside rear view mirror remains parallel to the windshield glass.
NOTE: The mirror mount is designed to detach from the button during air bag deployment. Excessive force or adjustment can cause the mirror to detach from the windshield.