At least for me, my Smart Home is constantly changing. I may rename a switch from “vanity” to “mirror” or something, in the tp-Link app or other manufacturer’s app. For some reason, google still insists on referring to the device by the old name, and doesn’t automatically figure out the new name, the way Alexa does.
The official FAQ/Docs say to unlink the account, for example, your tp-Link account, and re-link it back to Google and it will find all the devices again. This is a pain, because when the app is relinked, Google doesn’t remember what groups/rooms you had the devices in, so you have to move them all to the correct room. Real pain in the butt for a heavily automated home like mine.
Anyway, if you just say “ok google, sync my devices” it will resync and look for new smart switches or plugs you may have added to eWelink, Sonoff, tp-Link, Shelly, etc. The old ones stay where they were, and you just have to move the new ones.
It took a lot of searching and trial and error for me to find the right thing to tell the assistant to make this happen, but that command works. Hope this helps someone.