To turn off notifications:
- Navigate to device 'Settings'.
- Choose 'Notifications' .
- Find the game from the list and tap it.
- Turn off notification settings according on how you want to, or simply flip 'Allow Notifications' to OFF to turn off all notifications for the game.
- Completely close and reopen the game for changes to apply. If it still doesn't work the way you wanted you may also need to restart your device.