Connect a change node to the output of MQTT IN node
Set msg.payload to msg.payload.svalue5
Set msg.topic to power
Connect an MQTT out node to the new change node
The task you are doing is very basic knowledge of node-red, I recommend watching this playlist: Node-RED Essentials. The videos are done by the developers of node-red. They're nice & short and to the point. You will understand a whole lot more in about 1 hour. A small investment for a lot of gain.