If you are new to DIY, maybe consider calling in a pro to look at your situation and give advice, because misunderstanding what you are seeing is not uncommon…

Having said that, if you got everything cleaned down to the base materials, and if the wall surround is physically intact and stable under side load, there are several fixed you could undertake.

My favorite involves fiberglass and epoxy with whatever you want on top of that… but it’s complicated.