assuming you have a nest thermostat. Make sure you’re signed in to your new WiFi network
1 Press the thermostat ring to bring up the Quick View menu.
2 Select Settings .
3 Turn the ring and select Network.
4 Select the new Wi-Fi network by name and enter the new password. It may take a few moments for your network to appear.
Thanks for posting.
If both the existing and the new Wi-Fi networks are available:
If the original Wi-Fi network is no longer available or accessible:
Important: Once you complete the factory reset of the device, you'll need to set up your Google Home device again on your home Wi-Fi network and link a Google account to the device.
Hope this helps.