Epoxy? Well if its not been cleaned properly in the first place, you've a bit of a task now.
Does the residue feel rough under hand? If yes, then ltp solvex or nitromors will loosen the residue. You'll need lots of white scotchbrite pads and sponges too.
If it's a barely there haze, I'd suggest mapei kerapoxy cleaner, it's a trigger spray, but again you'll need plenty of pads and sponges.
This is exactly why epoxy should only be used with proper care and experience.
Get the tiler back to rectify it!