iphone hard restart

Hi there:

for the second and third generation of iPhone SE see this instructions

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the side button.

For the first generation of iPhone SE see this instructions

Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the side button. When the Apple logo appears, release the button.