You may need to use DFU mode if you're having trouble restoring your iPhone using recovery mode.
Using a USB to Lightning Cable, connect your iPhone to a computer running the latest version of macOS or iTunes.
Press the Volume Up button, then press the Volume Down button, then press and hold the Side button until your screen goes black.
Quickly press and hold the Side and Volume Down buttons for about five seconds. Release just the Side button and continue pressing the Volume Down button until your computer pops up with a message telling you that it’s detected an iPhone in recovery mode.
To exit recovery mode, press the Volume Up button, then press the Volume Down button, then hold down the Side button until the Apple logo appears.
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