@Yvonne G might be able to help.
If he were mine, I would very lightly see if that piece moves. If so I would find a good vet to have it glued or possibly put some liquid bandage on it. Also take away anything he could climb on or fall off of.
Also keep it clean and flies away
Check it out and if concerned go to a vet, ensure calcium and fresh veg is in their food as that is needed for shell strength same as your finger nails. As previously mentioned remove hazards.