If you've already changed to a different Wi-Fi network, try these steps:
1. Open the Google Home app.
2. At the top left, tap Add + > Set up device > New device > set up new devices in
3. Follow the in-app steps.
If these steps above don’t solve the issue, you’ll need to factory reset your speaker or display, then set it up again using your new Wi-Fi network and password.
Instead of factory resetting your speaker or display, if you're comfortable changing your router settings, you can change your new Wi-Fi network name and password in your router's settings to be the same as the previous ones. Your device should then automatically connect to the Wi-Fi.