This action can help if the game crashes or freezes, and it is also necessary to save progress correctly.
 
For iPhone X and later models, as well as iPads on iOS 12 or a later iOS:
  1. Swipe up from the bottom of the Home screen.
  2. Swipe left or right until you find the app you want to close.
  3. Swipe the app window up to force quit it.

For iPhone SE, iPhone 8 and older models, and iPod touch:

  1. Press the Home button twice to see the list of applications you've recently launched.
  2. Swipe left or right until you find the app you want to quit.
  3. Swipe the application preview up to force quit it.