Advice on Removing Gunite Blocked Return on New Pool Construction

I'm nearing the end of my new gunite pool construction. Everything is almost complete, equipment installed and running during plaster startup. However, we noticed that one of the five returns on the pool has no water flowing out. After using a camera to inspect, it looks to be plugged with gunite and the plumber somehow missed it when doing the plumbing. Either he didn't cover the back side of the pvc stub during gunite with tape, or he didn't bother to check if the pvc was clear when he finished the rest of the plumbing. What is the best way to clear this out. The pressure from the pump isn't enough to force it out, and I'm nervous if we block the other 4 returns and run it, it might be too much pressure on the entire return system. Some things to note:

1. there are five returns - I think we are fine if one of them didn't work, but hate the idea we paid for a new pool and they make this error

2. all the returns are interconnected - so there's no easy way to try to get to only this return line

3. we have concrete decking - none of the plumbing is easily accessible without digging/breaking the deck

4. the gunite is blocking complete flow - you can see its kind of rounded so there's no way to slip a wire past it

5. the gunite piece is about 2 feet deep into the pvc return

6. the builder tried using rebar to push the gunite and he said it slipped/moved back some

originally I was thinking maybe buying a 3 feet drill and trying to carefully drill the gunite piece. my worry is damaging the pvc and also not sure how to drill underwater unless we lower the water level. any other thoughts/ideas? the return system held pressure so there isn't any leak now. Should I just abandon this return and hope maybe one day it falls out?