How to remove old plastic pool deck sleeves
Select (or go buy) a cheap chisel - you don't want to do this with a nice one.

Wear safety glasses, the plastic is probably brittle with age and sun exposure.

You might want ot experiment with pouring boiling water into the hole first, to see if it makes this process easier - depending on plastic type, it may.

Set the chisel on the plastic, next to the concrete, and hammer it. Repeat as needed until the plastic sleeve is reduced to either plastic slices/shards you can remove, or possibly you may be able to remove the whole thing once you get one cut through it and can lever one of the sides inward from the hole in the concrete.