If an app isn’t working properly, you can try quitting it and then try to restart it. Doing so, may resolve the problem.

• ●  Open ​App Switcher
  • ○  Swipe up​ from the bottom edge and ​pause​ ​in the center​ of the screen.
  • ○  Double-click the ​Home ​button (models with the Home button).
• ●  Then ​swipe up​ on the ​app​ from the ​App Switcher​. This will completely close the app and its background process.
• ●  Simply tap on the app again to reopen it.