Force restart iPhone - Apple Support... ⬅︎⬅︎⬅︎ try this...
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Force restart iPhone 6s, iPhone 6s Plus, or iPhone SE
- Press and hold both the Sleep/Wake button and the Home button.
- When the Apple logo appears, release both buttons.
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support ⬅︎ see this...
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Try Recovery Mode...Connect your device to a computer. On a Mac with macOS Catalina 10.15, open Finder. On a Mac with macOS Mojave 10.14 or earlier, or on a PC, open iTunes.
Press and hold both the Home and the Top (or Side) buttons at the same time. Keep holding them until you see the recovery mode screen...
See full instructions in the link above...