My iPhone 11 has just stopped responding. I can’t shut it down and I don’t have a computer. Any ideas on how to reboot

Hello,

I recommend you to force restart your iPhone. Please reference below!

If your screen is black or frozen

If your screen is black or frozen, you might need to force restart your device. A force restart won't erase the content on your device. You can force restart your device even if the screen is black or the buttons aren't responding. Follow these steps:

• iPhone 8 or later: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Side button until you see the Apple logo.