cant factory reset my iphone six as i cant remember restrictions passcode

If you forget your Restrictions passcode, you'll need to erase your child's device, then set it up as a new device to remove the Restrictions passcode. Restoring your child's device using a backup won't remove the Restrictions passcode.

Use Restrictions to prevent purchasing on your iPhone, iPad, or iPod touch - Apple Support

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

forgot my passcode

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