You can get kits to repair them, Randy. Check at your local hardware or home improvement store.
Bondo makes a fiberglass product, however fiberglass needs a clear coat over it so don't skip it. The clear coat gives it durability. You could also see what products a boat shop have. They would have good tips and tricks to share as well.
There is repair kits at the home improvement stores you can try.
Is it cracked?
How is the tub damaged, or what exactly is it that needs repairing?
You might check your local home improvement store for a patch kit.
While it CAN be done DIY, I strongly advise against it. Definitely hire it out! https://bachelorettepadflip.com/2014/07/03/glazed-over/