how do i unlock erase iphone 5

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If you are referring to unlocking so you can use with a different carrier, only the carrier the device is locked to can authorize an unlock.

If you are referring to forgetting the 4-digit passcode used the lock the phone, you can only remove it by restoring the device.

If you are referring to unlocking a device that is Activation Locked, only the previous owner that locked the device can remove it from their account to allow you to activate it.