The fish has a swim bladder issue, sometimes caused by improper decompression. This symptom is unfortunately common in many Genicanthus. Your fish is in pretty rough shape right now, and certainly will not be able to compete in your display aquarium. It should be placed into an acclimation box (with hiding places), or better yet an established QT tank and allowed to destress on it's own accord. Make sure to feed small amounts very frequently if still accepting food.
If a retailer is properly conditioning fish this sort of issue would arise prior to being offered to hobbyists. This obviously directly impacts cost of fish as retailers have to hold onto it longer which comes with labor, saltwater and food costs. Unless you have an awesome LFS that properly conditions I advise only purchasing them from reputable vendors who do their due diligence for every fish. My closest LFS rarely brings these in, unless upon request, and pushes them out within days... as you can imagine sourcing Genicanthus for most people from places like this is a lose-lose.
