Quickly Add a New Smart Light to Your Google Home
If you have already linked your smart home devices through the Google Home app, this is video shows how to add a new light or smart switch to and existing partner app.
Prior to this make sure you have setup your new light through its own app and linked the device in the Home Control settings in the Google Home app.
Once that is complete use the following command to update you light:
“Sync my lights” or “Sync my devices”
Once the sync is complete you can then use other smart light commands you are use to. You can also go into the Google Home app and add nicknames or add the light to a room.
Source: Google’s Help Article