No offense, but there is more wrong with him than fin damage. He is of very poor quality, unfortunately. The dark color is due to peppering. The fish is a pigeon blood variant but with that much peppering it will always remain dark.
Notice that just above the eyes, his forehead appears "pinched." This is a sign that the fish is malnourished and is usually a sign of internal parasites or worms. Even if the fish eats, it probably won't put on weight. You'll need to worm it and maybe give him a metronidazole treatment to get rid of worms and/or flagellates.
The large eye indicates that the fish is behind on growth and is probably stunted. If you worm it and then feed it heavily, it may turn around, but chances are that it'll stay small.
In the future, look for fish with smaller eyes, less peppering, and that lack a "pinched" forehead when viewed head-on from the front. Healthy discus should be shaped like () that from the front.