Follow the steps to cast the Plex App through Chromecast:

1- Setup: Ensure your Chromecast-enabled device and your iOS device are connected to the same Wi-Fi network.

2- Install Plex App: Download and install the Plex app from the App Store.

3- Open Plex App: Open the Plex app and log in to your Plex account.

4- Select Media: Navigate to the media (movies, TV shows, etc.) that you want to cast from your Plex library.

5- Casting: Look for the casting icon within the Plex app. This icon is usually located in the top-right corner of the playback screen. It’s often represented by the Chromecast symbol.

6- Choose Chromecast: Tap on the casting icon, and a list of available devices to cast to will appear. Select your Chromecast-enabled device from the list.

7- Start Casting: After selecting your Chromecast device, the content should start playing on your TV.