rotarian

Hi All, I've been reading up quite a bit on this forum and I must say this is a very informative forum with great info on a wide variety of topics with regards to pool and spa. I recently hired someone to replace tiles in my in-ground pool and I've noticed the situation below after the removal of the jacuzzi tiles. Does anyone have experience with this type of damage as to why and how it happened? any recommendation on how to go about repairing it? I appreciate any input and advise you may give.