Pull up on the lever mounted to the bathtub’s overflow drain cover. This moves the tub’s built-in stopper to the closed position, so if you drop any parts down the main drain the stopper keeps the parts from falling further.
Remove the screw in the middle of the strainer by turning it counterclockwise with a screwdriver. Insert the tip of the screwdriver into one of the strainer’s openings, and then lift the strainer out of the drain opening with the screwdriver.
Insert the replacement strainer in the drain opening and turn the screw clockwise to secure the new strainer. If you cannot find a strainer that fits your tub’s drain configuration, you must remove the drain body and install a replacement as well.
Place a drain key in the tub’s drain body, with the textured end of the drain key pointing up. Turn the drain key’s dial until it expands to the point that it sits firmly in the drain body. Clamp a pair of slip-joint pliers onto the textured end of the drain key and turn it counterclockwise to break the drain body’s seal and remove it from the drainpipe.
Scrape away any of the leftover seal from the drain opening in the tub using a putty knife. Apply an even coating of silicone caulk to the underside of the new drain body where it contacts the tub’s surface, and then thread the drain body into the hole in the tub. Tighten the drain body the rest of the way using the drain key and the slip-joint pliers.