Restart an App or iPhone 6

If something isn’t working right, try restarting the problem app or iPhone.

Restart an app or iPhone 6 
Restart an app.If an app isn't working properly, you can force it to quit, then try reopening
it. Double-click the Home button, then drag the app up from the app switcher display to quit the app. Opening it again may resolve the problem.
Restart iPhone.Hold down the Sleep/Wake button until the slider appears. Slide your finger
across the slider to turn off iPhone. To turn iPhone back on, hold down the Sleep/Wake button until the Apple logo appears.
Force restart iPhone.If iPhone isn't responding, hold down the Sleep/Wake button and the
Home button at the same time for at least ten seconds, until the Apple logo appears.