How to tighten loose shower pipe??

The water pipe for my shower is loose. When I pull the on/off knob forward to turn on the water - the entire plate pulls away from the tile - and breaks any new caulking seal I put in place. Is there an easy way to tighten down the pipe again short of cutting into the wall?

Thanks

 

The shower valve is supposed to be secured by clamp fasteners to the wood structure. Either they did not do this, or it came loose. You could remove the round trim escutcheon and see if you can access anything that way. Otherwise, see if you can access from the other side of that wall.