Click Agree on the next screen that details the license agreement.You will see a warning: “Are you sure you want to restore the iPhone…” Click on Restore and Update.On your Mac you should now see a message indicating that there is a problem with the iPhone that requires it to be updated or restored.If you are successful eventually you will see an image of a Mac and a lightning connector on your iPhone that indicates it is in recovery mode. Unlike a usual restart keep pressing and holding the side button while the phone shuts down and starts up again. Shut down your iPhone by pressing volume up, volume down, and then press and hold the side button.
You may see a message that indicates you need to download an update to access the iPhone, in our experience the said software was unavailable from the software update server, so don’t worry about this.