If you've already changed to a different Wi-Fi network, try these steps:
If these steps above don’t solve the issue, you’ll need to factory reset your Chromecast, then set it up again using your new Wi-Fi network and password. If you're using Chromecast with Google TV, follow these setup steps instead.
Instead of factory resetting your Chromecast, 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.
Thanks for the help here, davidking.
Larspeter59, hope that helps but if you're still having trouble connecting your Chromecast to your network, please try to manually connect to the Chromecast SSID. Here's how: Go to the phone Settings > Open Wi-Fi and connect to the Chromecast SSID (Example: Chromecast1234, Living Room TV, Bedroom TV, etc.) > Go to the Google Home app and try to set up again.
Just checking in to make sure that you've seen my response. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.