Okay I know this is going to sound incredibly weird or just wrong
But honestly what I did for practice without hurting birds is practicing on a few dead ones, immediately after killing. Not everyone culls their own stock I know, but, it taught me how much to pull the wattles without cutting the main neck skin, and how to do the earlobes, and even the comb decently fast without making mistakes, thus making the experience quicker for the bird. That way if I make mistakes, there's no-one to go through the pain and bleeding.