Tap tap. Take a screenshot. Or go to the Home Screen. Or open Control Center. You can set up Back Tap to perform an action when you double-tap or triple-tap the back of your device.

To learn more about this topic visit the following articles:
Use Back Tap on your iPhone: https://apple.co/3ejoth1
About the Accessibility Shortcut for iPhone, iPad, and iPod touch: https://apple.co/3b7cXDI
Use AssistiveTouch on your iPhone, iPad, or iPod touch: https://apple.co/2PS5lgV

Additional Resources:

Contact Apple Support for iPhone: http://apple.co/iPhone

To subscribe to this channel: https://www.youtube.com/c/AppleSupport

To download the Apple Support app: http://apple.co/2hFtzIv

Apple Support on Twitter: https://twitter.com/AppleSupport

For more videos, go to Youtube Apple Channel