I was so worried ? I thought it was shell rot or some type of fungus thing, I cleaned his underbelly with a soft toothbrush because he had poop stuck on there, I don’t think I hurt him cause he was happily eating straight afterIt does look pretty normal, that is where the yolk sack is attached when they hatch. It slowly absorbs and the shell seals up but it can look weird for a while.
You probably have been shown this but here is the care sheet just in case - The Best Way To Raise Any Temperate Species Of Tortoise | Tortoise Forum