I made one with a piece of pool vinyl and some clear silicone. I ran a bead of silicone around the perimeter of the drain hole and placed the blue pool vinyl over the silicone. I used a piece of duct tape to hold it in place until the silicone set. When I want to remove the over flow plug, I just peal it away as the the silicone makes a semi permanent seal which is easily removed if needed. You could try fashioning a more semi permanent plug made from the silicone

On my old pool there were threads in the pipe for the overflow. I just got a threaded plug and stuck it in there.

just grout it in as it should be @ the top of your tile line. I would try to match the tile but don't worry about that. Lower the water and EZ patch it. Your set. Cheers