Looks like shed skin that just didn't come off. You can take a pair of tweezers and pull it out if you feel it necessary. It may come off on its own tho. I'v had to do it before sometimes it just happens. My gecko shed perfectly fine after that one time of having to pull it out so he should be fine just may need a bit of help this time. Good luck.
I agree - looks like stuck shed. I would give him a soak or two and rub gently or use tweezers if you're comfortable with that. It should come right off. If it persists or gets worse it might be something else and I might find a vet to head to in that case.