How do you remove a wire from a push-in fitting when there is no release opening?
Unless the wires are way too short, just cut them off - it's not worth wasting your time for 1/2" of wire. You can use wirenuts and add a pigtail if you need more wire. If the wires are way too short, and the circuit is dead, put on safety glasses and use a hammer or locking pliers or a bolt cutter to smash the crap receptacle and release your wires quickly. Life is way too short to fuss with a rotary tool cutting them open.