not working

Did you already try to force restart the phone, as described in this article?

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If iPhone isn’t responding, and you can’t turn it off and on, try forcing it to restart.

Force restart an iPhone with Face ID, iPhone SE (2nd generation), iPhone 8, or iPhone 8 Plus

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 button.

Note: If iPhone still doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen.

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copied from: Force restart iPhone - Apple Support

Try and Force Restart your iPhone EXACTLY as shown below and see whether that resolves the issue:

• Press and quickly release Volume UP button
• Press and quickly release Volume DOWN button
• Press and Hold the SIDE button until an Apple logo appears and then release the Side button (Can take up to 20 seconds. (DO NOT release Side Button when invited to Slide Power OFF). 

Axel F.

In that case, this looks like a hardware issue, and the iPhone has to be serviced by Apple or an Authorized Apple Service Provider next to your place.

Apple - Find Locations

Did you try to connect the phone in recovery mode to your computer, to set it up again?

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

You're welcome 🙂

Good Luck!