Tub repair? Fiberglas...

I think place like Lowes sell patch kits. It shouldn't be that hard even for those with little mechanical ability.

My unit has a 2 section shower stall that looks like plastic, if it had the issue I'd look into replacing it. If you don't want to go that route you could use white duct tape or some such. Or cut a piece of scrap plastic to fit and use silicone sealer to hold it in place, I did this to cover an old gas line hole through my house siding, 25 years ago.