Hi,
If I understand correct you have installed Zigbee2mqtt firmware on an Itead Zigbee dongle?
If you are using Zigbee2mqtt then you can node-red-contrib-zigbee2mqtt for easy implementation.
Or you can make your own with this simple mqtt example.
The sample is not specific for Xiaomi switch, but it should not be to difficult to adapt.
[{"id":"cb09fd.432436","type":"mqtt out","z":"6ebb4e1a.90e7","name":"","topic":"zigbee2mqtt/Salontafel/set","qos":"","retain":"","broker":"e992f40a.2e8898","x":1020,"y":1420,"wires":[]},{"id":"250e1812.045c2","type":"inject","z":"6ebb4e1a.90e7","name":"","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"Device\":\"MySwitch\",\"send\":{\"Power\":\"On\"}}","payloadType":"json","x":700,"y":1420,"wires":[["cb09fd.432436"]]},{"id":"e992f40a.2e8898","type":"mqtt-broker","name":"","broker":"192.168.1.127","port":"1883","clientid":"","usetls":false,"compatmode":true,"keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthPayload":"","closeTopic":"","closePayload":"","willTopic":"","willQos":"0","willPayload":""}]