If you're casting from an Android phone or tablet device you can activate subtitles by following the steps below:
1. Make sure you're in the Tubi app and that you're connected to Chromecast.
2. Tap on the Chromecast controls at the bottom of the screen:
3. Tap on the "CC" button to the right of the play button:
4. Tap on "English Subtitle" and press OK.
Now subtitles will be activated on your big screen!