phone states iphone unavailable how can i fix

Click here and follow the instructions. Restoring the iPhone requires plugging it into a computer with iTunes 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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See instructions in: How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

If that option is not available, you will need to use a computer. See:

If you forgot your iPhone passcode - Apple Support