Itf it’s like other GM cars that I have known, there is a wire clip on the backside of the crank. Push the door liner back while pulling out on the handle to see the clip. There is a special tool to grab the clip but I just used a piece of coathanger wire with a short hook bent on the end. A small flat bladed screwdriver might work too. Watch the clip carefully as it might go flying and use safety glasses too.