Is there a trick to removing the control knob in shower. I know there is a cover plate, I just can't figure out how to pop it off. Do I need a special tool to get that plastic cover off. I tried a flathead screwdriver, but the tip is too fat.

Take a knife blade and pop the cover off. Underneath you should find a screw that secures the handle. Remove the screw and pull the handle off. Rehards, Tom