Press and hold the side button and either volume button until the power-off slider appears
Drag the slider to turn off the iPhone
If the iPhone has a Home button, press and hold the side or top button until the power-off slider appears
Drag the slider to turn off the iPhone
If the screen is unresponsive, press and quickly release volume up, press and quickly release volume down, then press and hold the side button until the Apple logo appears and the device restarts
To fully power off after a forced restart, use the power-off slider when it appears again