How to send the command for setting the multicast address of the node group to the nodes

If you are using FUOTA, then ChirpStack will do this based on the Remote Multicast Setup specification (TS005). If you want to use just multicast, you could use the same Remote Multicast Setup payloads, but please note:

• Your device must support this TS005 specification (of which there are multiple version)
• You need to construct these payloads yourself and then enqueue these into the device queue

There are also many devices that do support multicast, but use out-of-band configuration to setup the multicast group.

To create the multicast group in ChirpStack, please see the Multicast groups tab under the application: