How can I factory reset my iPhone 11?

Click here and follow the instructions. Restoring the iPhone requires plugging it into a computer with iTunes or Devices installed, or a Mac running Catalina or newer.

If there's an option to erase it, you can use that instead.

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It would help if you provided more detail such as the exact wording of the error message. It would be a pity if you erased the device entirely if all it needed was a much simpler solution. For example, this: If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support