if it is a serious nick that may allow moisture in or its just too deep then clean the damage and put some masking tape along the damaged sidewall and squeeze in some epoxy. Most of what i've seen is a light grey / white colour so it may not match up or be pretty. After it sets file and sand down the epoxy so that u can sill get at the edges to tune them if u need to. Tough to make it look pretty. It can be a messy job.
Some people actually round off the top sheet at the side edge to prevent drastic chips when skis hit.