Here is a video on doing a half turn tension on the magazine spring.
Doing a full rotation is much easier, you just need to loosen the screw on the bottom of the mag so you can lift the red plastic part, then spin it and carefully lift it over the magazine rotation stop. You will know exactly what I mean when you see it. You will most likely need to experiment to figure out what your Blitz needs to cycle properly. If full auto works when blank firing the gun is running perfectly as the internal push force will be higher (for easier cycling) when a projectile is blocking the exit.
Here is a adapter video from DonnyFL