How to get rid of the discoloration?

Previous owner apparently used to use Apple cider vinegar in his baths so it etched our cast iron tub. Now it looks like this 🥴😬 any recommendations on how to fix it? Also any suggestions on what to do with the soap ledge in the wall? We aren’t going to redo the tile, and water always gets stuck in this soap ledge and it gets moldy and gross