It's hard to tell. Looks like an injury. If not an injury, then flukes. So, this is what I would do.
1) If he is breathing hard, having serious trouble my go to would be an emergency freshwater dip. You take RODI water, put a squirt of tank water in it...just a very little bit to buffer. Then, you drop an air stone and correct for temperature. I would then add the CBB for 5 mins IF HE TOLERATES IT. I would try to do more than 3 mins but less than 5.
2) No rush or urgency. Prazipro! I would setup a small tank with PVC plumbing pieces and a HOB filter. I would then dose Prazi...
That's assuming it's flukes. If you do a freshwater dip, you will see the flukes on the bottom. They are clear...
