I’d like you to try the troubleshooting steps below:
- Check for system updates. Go to Settings > My Fire TV > About > Check for System Update to ensure your Fire TV is running the latest software.
- Go to Settings > My Fire TV > Restart.
Enable Close Captions on Prime Video on Fire TV see here.
- While a video is playing, press the Menu button on the remote, then select Subtitles. Select from the available language options. To return to the video, press the Menu button.