While previously, users can force reset their iPhones by holding down on the iPhone’s power button and the home button simultaneously for 10 seconds, for iPhone 7 and 7 plus, try this instead:
1. Press and hold down the power button located on the right side of the iPhone 7.
2. While holding down the power button, press and hold down the Volume Down button on the left side of the iPhone 7.
3. Hold down both buttons until the screen turns off. After a few seconds, the screen would come on, displaying the Apple Logo.
4. Wait for your iPhone 7 to completely boot up.