For Android:
- Go to Settings>Apps>Manage Apps.
- Select the app and tap on "Shut down".
- Go back to the home page and restart the game's app.
For iOS:
- Press on the Home button fast twice.
- All the open apps will appear on the screen; slide right or left to find the app.
- Slide the preview image of the app up.
- Go back to the home page and restart the game's app.