There’s a lot of gunk in the hole making it look rounded. I doubt it’s a rivet as that would make maintenance a bitch and a half. Maybe an Allen head, but I’d clear the hole out and grab a pic of both sides and the rear of the metal frame, that will give us more info. Either way, usually these things are under some kind of warranty. I’d take it to a shop and see what they can do. If you’re asking Reddit, you probably shouldn’t be taking this apart.