Since I bought a new Z-Wave controller recently (ZME_UZB which support Z-Wave PLUS) I was now facing an issue there I needed to remove a device from my old controller (ZME_Z-StickC). However, I did not have the old controller available.

Including Z-Wave devices that are already registered with another Z-Wave network does not work immediately. The device needs to be factory reset first.

Resetting the device is easy also without the original controller, once you know how:
Simply use ANY controller and put into EXCLUSION mode. Afterwards, follow the instructions for exclusion of your device (e.g. tripple-click one of the buttons on my switch).

After that, the device is excluded (from its original network, although another controller triggered the exclude) and thus reset to factory defaults. Once that has happened inclusion works again.