This article explains the major different types of iPhone 12 resets and how to do them.
To reset iPhone 12, do these things:
Press theVolume Downbutton andSidebutton together.
When theslideto power offslider appears on the screen, let go of theVolume DownandSidebuttons.

Slide theslide to power offslider to shut down the iPhone.
Wait about a few seconds for the iPhone to turn off.
Once the iPhone is off, wait a few seconds and then press theSidebutton again.

When the Apple logo appears, release theSidebutton and the iPhone 12 will restart.
Here’s how:
A hard reset is sometimes also called a force restart.
Press theVolume Upbutton and release it.

Press theVolume Downbutton and release it.
Press and hold theSidebutton (ignore theslide to power offslider).
When the Apple logo appears, let go of theSidebutton.
Wait for the iPhone 12 to restart.
To solve some problems, you may need to reset those parameters.
To do that, go toSettings>General>Reset.
If you don’t do this, your iPhone 12 will beActivation Lockedto yourApple ID/Apple Account.
Scroll to the bottom of the screen and tapReset.
TapErase All Content and parameters.
If prompted, enter youriPhone passcode.
Wait a minute or so for your iPhone to delete everything on it.
When your iPhone restarts, it has been reset to factory controls.
Press and hold theSidebutton andVolume UporVolume Downbutton.
Then, swipe right and left to find each app you want to close.
To terminate the app, swipe up and off the top of the screen.
There is no way to close all apps at once.