The Nest Wifi unit must be connected to the internet for you to be able to manage it through the Google Home app. Sounds like you need to factory reset it using the physical button.
The factory reset guidance has been broken for over a week now, at least for me. If it works for you, look for info on factory reset using the physical button:
If I remember corretly: Let the Nest Wifi unit power on and go to a stable state (solid red light for you apparently). Then hold the physical button located under it until the LED light turns solid yellow. Then release the physical button and let the unit factory reset itself. It can take up to 10 minutes. When the unit is ready for setup it will pulse white.
Before you can set it up again in the Google Home app you have to delete the existing network in the Google Home app.
I don't work for Google.
