Mark the location of the studs on the wall behind the shower faucet, using a stud finder. Drive a finishing nail through the wall around the stud locations, finding the exact edges of the studs, and mark the locations on the wall.
Measure the height of the shower faucet, inside the shower. Mark the same measurement on the wall behind the shower’s faucet, adding an additional foot. Cut the drywall between the studs, up to the height mark you made, using a drywall knife.
Pull away the drywall you cut out, exposing the shower’s faucet and water pipes. Measure the height and width of the opening you cut, and then cut a 1/2-inch thick board to the same dimensions.
Attach a handle of your preference to one side of the board, using 1/4-inch long wood screws. Press the wood panel into the opening in the wall, giving you quicker future access to the faucet.