iPhone Activation lock

We cannot help you remove Activation Lock and Apple won't help you either. The only person who can remove Activation Lock is the person you bought the phone from.

Here is a link you can share with them --> How to remove Activation Lock - Apple Support

If they cannot do this, the ONLY other option they would have is to provide the original purchase receipt clearly showing the serial number of the iPhone it to Apple and then and only then would Apple be willing to help.

If they don't have it and they cannot remove Activation Lock, get your money back as the phone will be useless to you.

Read this as well --> The All Too Common SAD Reality of Buying … - Apple Community

If they don't know, or won't help you, this phone will be useless to you. There is nothing anyone here, nor Apple can do to remove this lock. It is meant as an anti-theft mechanism. Get you money back from your "friend."