Step 2 · Create Wall Access
Go to the wall directly behind the shower valve. Use a stud finder to locate the studs on either side of the plumbing pipes. Mark a rectangle for your access panel, typically about 12-16 inches wide and tall enough to give you ample room to work. Use a level to ensure your lines are straight. Carefully cut along the marked lines using a drywall saw. Remove the cut piece of drywall and set it aside; you can reuse it to patch the hole later.