A:Answer Having a new modem means having a new source of IP address for your internet connection. Since there's a change in source, you will need to factory reset the Google Wifi and re-setup. Here's a guide on how to factory reset: https://support.google.com/wifi/answer/6246619
Also, if your modem is a modem/router combo, we recommend putting it in Bridge mode or disable the Wi-Fi functionality to avoid double NAT related issues. You can learn more about Bridge Mode here: https://support.google.com/googlenest/answer/6240987