We’ll assume, for the sake of the tutorial, that you are able to access the previous Wi-Fi network as well as the new one. If you’re unable to connect to the old one, you’ll need to do a factory reset. Than again select the network form the list. 
Although while selecting Network keep one thing in mind that Chromecasts can only connect to 2.4G networks. Devices that can connect to 5GHz networks or Ethernet will be able to connect to Chromecast provided they are on the same router.
- Open the Chromecast app on your Android or iOS device
- Search and connect to the Chromecast
- Open the settings page
- Tap the Wi-Fi network
- Select the new network from the dropdown menu
- Enter network password
- Save
Note that you will find a message advising that your mobile device and Chromecast will not be on the same network. Simply connect your device to the proper network and you’ll be in business.
