Activation lock on a used Iphone

If a used iOS device has been 'Activation locked' then only the previous owner can unlock it, either by providing you with the account ID and password, or by removing it from his list of devices (as he should have done before selling it).

If you are unable to contact him to do this then I'm afraid you will not be able to use the device - there is no other way of unlocking it at all. Apple cannot unlock it for you, nor find the previous owner for you, and neither can the websites that offer to unlock it for a fee: these are scams.

You should if possible return it to wherever you bought it and ask for a refund as in this event the device is completely useless.

Read this user tip I wrote --> The All Too Common SAD Reality of Buying … - Apple Community

Bottom line: The phone is 100% useless to you. Apple won't help you. We can't help you. Get your money back, recycle it or use it in one of the ways listed in the user tip link I provided.

To summarize the above: "You don't".