What is the reward for patience? Leave the pieces in place until they are nicely browned, resisting the inclination to prod them and move them about and check them every 30 seconds, and you will be able to detach them easily from the bottom of the pan. But this might take five minutes. You’ll notice the same thing with other meats. Breakfast sausage is a good example. Put a patty in the pan and it sticks like glue. But as it cooks, it begins to brown and form a crust, and shortly you can move it with ease.
Also, make sure the oil is hot before you put the chicken in, use enough oil (the tendency to stick decreases as the amount of oil increases), and dry the chicken with paper towels before you add it to the pan. A previously frozen chicken might need to be dried a little more thoroughly, but is otherwise no more inclined to stick to the pan than one that has not been frozen.