How to delete other Apple ID

If this Apple ID, on this iPhone, is not yours, you need to contact the original owner to have them remove their ID from the phone. Otherwise, this phone will be useless to you.

Ref What to do before you sell, give away, or trade in your iPhone, iPad, or iPod Touch - Apple Support

Head to privacy.apple.com and sign in to your account.Click Request To Delete Your Account.Choose a reason for deleting your account and click Continues