Hi there and welcome
To do this
Start playing the video.Press the Menu button on your Amazon Fire TV remote or the Fire TV Remote app.Select Turn Captions On.
After you turn captions on, use the left or right arrows on your remote trackpad to set captions options, including font size and color scheme. Your selections apply to all videos you play until you change them
If you have any problems, or would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.