You have to replace at least the top tile.

replace the tile that was cut wrong. No other way.

Well you remove the fixture trim and pop the tile out, you should have tile left if you ordered 10-15% more than what you needed...(standard practice)...if you do not then go to the tile store where you purchased the tile from and order two or 3 pieces as samples bc they will usually sell you a full carton.

Based on a second look you will most likely need to remove two tiles, the top and the one below. So order 4 tiles.

You use a tool to carefully removed the grout around the tiles in question. You try not to damage the membrane if it was placed on top of the cement board. You can section the tile, too. Since you have a hole to work with you should be able to get underneath the pieces and pry them off. Fix the membrane if necessary and reset new tiles.

At the right vertical edge it appears to be a Kerdi mixing valve gasket installed underneath. That is where they went wrong. Tile was cut to this gasket. Diverters are always smaller. Hopefully Kerdi board was not used as the paper face will probably come off with the tile. This repair will be tricky if this board was used.

You might be able to just replace the smaller square escutcheon with a larger one (like the one on the bottom). Looks like it might fit.

Schluter is the manufacturer. Kerdi is the system. This is the reason for my previous post.This is the installers error plain and simple. Now the question is what wall board was used?

Before you tear into the tile I think you should call the manufacturers of the shower system and see if they can send you you that larger square escutcheon as nidnay suggested.

When I had an issue with a Moen shower valve that stuck out too far in spite of the plumber following the Moen instructions, (found out after the fact that others also had issues with the Moen instructions) Moen sent an adapter piece at no charge.

Since it looks like an installer error, I wouldn't expect the larger back plate to sent be free of charge but whoever made that mistake should pay for one.

YOU do not cut out one piece of tile at all. The tile guy does it, and it's very simple. This is a mistake I see alot of. The round plastic piece that's left on the valve after installation-- tile installers think you need to cut to that piece. That's there to make sure the DEPTH of the valve is correct-- that piece should be flush to the face of the cement board (+/- 1/4"). Once that's determined as being right, that piece of plastic means nothing. The ONLY things you have to leave open, are the valve itself, and screw holes for the faceplate. But instead of having a 4" diameter round hole, all you need is about 2 1/2 " of square hole to leave everything open that needs to be. Very rarely is that not enough.

valve wise, the first thing a tile pro does is check the escutcheon plate//trim then remove the ring and chuck it The only exception is if im on an exterior or wall with no back access. Theres so many valves out there but when you have been in the game a minute you dont make these errors. You leave notches/ cuts for the screws to mount . And CTEC brings a great point about how to reconnect waterproofing with the proper repair.

I don't know about where you are, but up here in Maine, if you get on the job and the valve is on an exterior wall, you get the hell out of there, because that shower is going to be trouble, and you don't want any part of it!! LOL

my bad. :-) (re location)