To turn on subtitles/closed captions on Amazon Fire TV/Stick you must enable them while the movie or TV show is playing.
- Open the Tubi TV app.
- Select and Play the video you'd like to watch from the Tubi TV home screen.
- Press the Play/Pause button on your Amazon Fire Stick/TV remote.
- Select "CC", which will appear at the bottom right corner of the screen.
- Select "English" and subtitles / closed captions will be displayed on your screen.