Shut off the water supply to the shower. There are cut-off valves for the hot and cold water behind the shower wall. The shower wall usually has an access panel in the adjoining room.
Place a towel or sheet over the shower drain to prevent losing small parts down the drain and to protect the shower floor.
Remove the screw securing the shower handle to the faucet assembly. The set screw requires either a hex wrench or Phillips screwdriver for removal. Pull the shower handle away from the faucet assembly.
Pull the dome cover away from the faucet spindle. Some dome covers have a nut on the top, requiring an adjustable wrench for removal. Once the dome cover is off, the spindle cap with the two flat sides is visible.
Turn the spindle cap counterclockwise with the adjustable wrench, and remove the cap and spindle from the faucet. Shine a flashlight inside the threads of the faucet cavity, and clean the threads with a soft cloth.
Wrap the threads of the spindle with plumber's tape. Thread the spindle back into the faucet cavity. Tighten the spindle cap with the adjustable wrench.
Push the dome cover over the spindle cap and secure with a nut, if your dome cap uses a nut. Place the center of the handle over the end of the stem and secure with the retaining screw. Turn the water back on to the shower.