Press and hold the side button until the Apple logo appears
If your iPhone has a Home button, press and hold the side or top button until the Apple logo appears
If it does not turn on, connect it to a charger and try again after a few minutes
If the screen is frozen, press and quickly release the volume up button, then press and quickly release the volume down button, then press and hold the side button until the Apple logo appears
If the battery is completely drained, let it charge for at least 15 minutes before trying again