the plastic piece is falling down? or the switch is falling apart? (your title says controls, but you seem to be talking about the plastic covering which holds the switch, is falling down.
If your talking about this. Take a small flat screwdriver and pop the middle of the light switches down (they switches that covers the map lights in the plastic piece) (they pop out) there are 2 philips screws located behinds the light bulbs...or there should be...check to see if they are there...these are what holds the piece up...that and the metal clips in the rear of the piece. If they are there, unscrew them and slide the whole plastic piece towards the rear of the car...this "unclips" the back portion of the covering. Be careful as there are 2 wiring clips. One for the moonroof switch and one for the map lights...
Hope that helps..