I've noticed pieces of rebar falling near the skimmer entrance. When I look right under the coping near the skimmer entrance, I notice that what appears to be concrete has been falling away and the rebar is rusted.

I'm looking to repair this myself. I'm guessing I need to pull the coping back and redo the concrete. I was planning on using regular mortar. Can use regular mortar? And any other recommendations would be appreciated.