There are no screws, just one retaining clip and a tab on the top and bottom of the back side. Take off the fuse access panel and look up there, you'll see what I mean. Push with your thumb/fingers from the inside out on one of the tabs followed by the other. It'll undo itself and come loose.
side note: what's your problem and why do you think it's the button?
The switches occasionally go bad, but they're not permanently dead. What typically happens is the contacts on the inside get dirty or contaminated, and no longer have the electrical continuity they once had. Opening them up and cleaning them up, maybe lightly hitting the contacts with high-grit sandpaper, should fix them good as new.