Identify what stopped working
If the app will not launch, test whether another installed app starts. If it opens but cannot sign in, keep the login error separate from the launcher symptom. On supported Fire TV software the relevant menu is typically under Settings, Applications and Manage Installed Applications.
Work through the reversible actions
- Note the player name, model, operating system and free storage.
- Restart the Fire TV and retest the same app.
- Check the supported installation or update route from the app publisher.
- Clear its cache where available and retest.
- Use Clear Data only after confirming that you can restore the player account and settings.
When to take it further
If several apps fail after a restart, check system software, storage and connectivity. If one player alone continues to fail, give its developer the device model and player version, the last working date and the result of each action.