Casambi enabled luminaires/devices can be part of (paired to) only one network at a time. If you would like to add a device to a different network then you first need to unpair the device from the network it is part of and then add it to the new network.

Note that unpairing a device from a network will mean that it loses all settings specific for that network (i.e. it resets to its factory default status).

See also:

"How do I pair a Casambi enabled device?":

"How do I unpair a Casambi enabled device?":