1- Connect your iPhone/iPad to a Wi-Fi network. 

2- The iPhone/iPad you are using to cast must be on the same Wi-Fi network as your Chromecast or TV with Chromecast built-in and enable local network access permissions for iOS 14 and above. 

3- You must be running the latest version of the app. You can always double-check that you are on the latest version by visiting the Apple App Store and checking for any available updates. 

4- Launch the app

5- The app will auto-discover all available devices on the same network. Tap the device name to connect.