Any ideas on fixing the surface once clean?

"Any ideas on fixing the surface once clean?"

You don't. You replace the tile, throw a gob of caulk on it and live with it until you redo the bathroom.

After the tile is "clean clean" the surface of tile will look better. Was the tile originally a gloss or mat finish?

Matte finish. Replacing isn’t an option, it’s a rental.

You really cannot fix chipped tile any other way then replacing. Silicone or epoxy may hide it but if you did it, get ready to lose your security deposit.

Give the Oxy Clean a try and report back to us how the tile & grout looks afterward. Use a good stiff brush in cleaning or use a grout brush.