(If you have an iPhone 8 or older, just hold down the side or top button, then drag the power off slider.) If your iPhone isn't responding to that, then you'll want to force a restart. Resetting ...

Turning off an iPhone 8 Plus or earlier is slightly different. 1. Press and hold down the side button. 2. When the power slider appears, swipe the power button inside it to the right. 3.