If you are not worried about looks or smooth flow, then it is easy. Just sand or grind it down all around the damaged areas and into the good material about 1" or so. A smooth taper (scarf repair) is probably better than steps as the previous post shows, but the principle is the same. Use glass fabric rather than mat, and S-glass (for strength) if you can find it. I prefer epoxy resins and U.S. Composites sells gallons pretty cheap compared to West Systems. The slower curing types will give higher toughness. You may be able to find details in the http://home.iitk.ac.in/~mohite/Composite_Repair.pdf
or just google "composite repair". You can repair it with a surface build-up then go back and sand it smooth and paint to get a nice finish just like any body-work.