As there are two ways to factory reset a Google WiFi Pro, in this video we demonstrate both methods. However it should be noted that Google do not recommend that you perform a factory reset directly from the device.
Note: We suspect that while you can perform a factory reset directly from a Google WiFi Pro. If the router is not connected to the internet. The router will not be able to de-authorise itself from your Google account. This has a knock on effect, where a ghost instance of your router will appear in the Google Home app. So you will need to wait for up to six months, before Google will automatically remove your old WiFi network from Google Home.