Under the shifter boot there is a manual park-release lever. Pop the boot up gently (no tools needed), press the lever down, and the shifter will move to N with the engine off. Keep the handbrake on until you are ready to roll, and release it only when steering with the wheel is possible. On E9x cars the release is at the front-left of the selector — if it feels stuck, wiggle the lever while pressing the brake once. This is exactly how the tow truck will do it, so doing it yourself saves time.