Start playing the video.
Press the Menu button on your Fire TV remote or the Fire TV Remote App.
Select Subtitles and Audio.
Select the Off button under Subtitles and Captions. Then select an available subtitle language from the options on-screen to turn captions on.
Tip: You can then set preferences for the way subtitles display, including text size and style. You'll see a sample of your selected options on-screen.
Press the Menu button again to return to video playback with subtitles on