Start with removing the bad piece with a tight-fitting metal pin. Pry it out gently by turning round and round with the metal pin. Clean up the hole…
Select a new one, make sure it is well-fitting!! Or, if you are lucky and it didn’t break, then it can be re-used by rotating it over p.ex. 90°, or 180°…. Glue it, and let it dry.
Apply shaping with a hand-made mill.
Metal pins, hand drill & hand-made mills.