Remove shower pan. If necessary, use hammer and cold chisel to chop out any tile that extends under the pan. Attach the strainer to the drain hole in shower pan. Vacuum the subfloor clean of all dust and debris. Check floor with a 4-foot level; install shims to create level surface. Set shower pan into place and check for level.

Open up the lower layers of the shower wall, loosen up the shower pan then disconnect the shower drain before removing the shower pan. Replace the shower pan by positioning it on the shower floor, connecting the shower drain then placing it on the shower floor before covering up the wall around it.