Same as a regular EPS core/epoxy surfboard. Grind out the busted up area making sure to leave a bevel around surrounding good glass to blend repair back. Prepare a small batch of epoxy resin. Take part of the batch and thicken to peanut butter so it won't run at all- it has to stand up on it's own. Fill the hole just below surface level then take the rest of the batch and saturate 4 layers of concentric 6 0z. (or whatever you have) fiberglass cloth, 4 layers to aiding in fairing it back, you don't want a lump or to sand through the glass. Remember,the glass is the strength, not the resin or fill. Let it set over night, then sand the repair as level as you can but do not touch the board with grit, only the repair. Carbon glass jobs almost always have a fiberglass cap to bury the carbon but still be extra careful not to touch the rest of the board. Caveat: do repair in the evening as the surrounding air is cooling. Never seal an EPS shape in the morning as it is warming because the warming air in the board will expand and blow the repair off. After 5pm if not in a temp contolled area. Never use epoxy resin/filler more the 1/4" thick on an even slightly warm day because it will cause a runaway hotspot that will melt the EPS foam and cause a major disaster. Don't ask how I know this. Never stick an EPS core epoxy repair job in the sun, it will heat up and blow the repair off because the cures slowly, even fast kick . Sometimes takes a try or two to get a repair without a void, thick filler helps. Epoxy loves 70 degrees, hates over 80 and under 60. Oh, and black spray bomb to match it up. Unless you are OCD and have to have a carbon repair, then use carbon on the bottom of the repair under the fiberglass. You can fair out any dip or dent with polyester resin and fill if you like. Carbon is easy, try a kevlar lamination repair one time- those are a nightmare.
Or fill it with epoxy suncure and hope for the best if it is a tiny ding, just make sure to scratch it deeply to get some tooth..