Heater/AC Controls

I'm getting ready to attempt to repair the heater/ac control buttons on my 72 Dart. It looks like they are all pused in, but don't return to the out position. I have located a new set from a 70 donor car. Has anyone had experience with pulling the factory air from below the dash, and removing the controls. It looks like the trim panel has to be removed from the inside. (There are no screws on the outside). Help?