YouTube Moen shower valve repair. There are quite a few, and several are really good. My daughter, and her mechanically sterile mother, did the one at their house and only had to face time me once. They had to pull it back apart, because they put the cartridge in 180-degrees out of whack, and it had th hot and cold reversed. Which is just about the only thing you can get wrong. A Moen cartridge tool is really handy to have. And putting a liberal amount of plumbers grease on the cartridge makes it easier to get in, and lots easier to get out next time.