In a fiberglass corner shower shell.
What I have is an old leaking rusted
Shower valve assembly. It leaks from the
Shower head that is a hand sprayer with a wall mount from the sprayer. It also leaks around the both the hot and cold water wall mount knobs. The cold water knob the sleeve that is against the wall hangs loose. Won't stay put.

So I need to replace the shower faucet/knobs/valves behind the fiberglass shell without damaging the fiberglass hopefully?

Can I buy the assembly complete?
It is called a??

What is my best plan of attack to get the shower valve assembly out of the fiberglass wall?

I need to shut the water off for the building because it being a shower it has no shut off valve like you have for a bathroom sink or toilet. Unless I can turn off the water to that unit by??