how to set the MQTT topic and JSON content to send a multicast downlink command to a group of mote?

ChirpStack (v4)
1

I know that you can use the following MQTT topic and JSON content to send a unicast downlink command to an end device:
Topic: application/d92358eb-ba9b-4a36-8404-d17befc80467/device/fe03620000098721/command/down
{
“devEui”: “fe03620000098721”,
“confirmed”: true,
“fPort”: 10,
“data”: “MTIzNDU2YWJjZGVm”
}

But I don’t know how to set the MQTT topic and JSON content to send one multicast downlink command to a group of terminal devices, can anyone point me out?