How Can I unlock iphone: iPhone Locked to Owner
Can I unlock this phone without owner?
iPhone 7 Plus
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You can't unlock the iPhone, but the original owner can. It is activation locked. This is an anti-theft device. See Activation Lock for iPhone, iPad, and iPod touch - Apple Support
Read How to remove Activation Lock - Apple Support for actions to take to remove the lock. They all involve getting the owner to unlock the device.