Cosmetic or structural damage to Carbon Crank Arm

A lot of carbon cranks are running around like that. It's almost certainly harmless. If you can dig a fingernail in and feel jagged fibers that might warrant smoothing it down or filling it in and sealing it, but for the most part it can be ignored. Some people use something like heli tape to protect that area. That's reasonable if you're doing the kind of riding that causes impacts here to begin with. If it's bugging you, you can get an opaque protection sticker to cover the damage.