Access the Yahoo! or non-Yahoo! email that you provided to Yahoo! as the point of contact for the situation and look for an email from Yahoo!
Yahoo! uses confirmation codes to verify a variety of actions taken by Yahoo! customers. A confirmation code can validate an email address or mobile communications number when you register for or set up a Yahoo! service. In addition, it can prove to Yahoo! that you want to change or end a service. Typically, Yahoo! sends confirmation codes electronically to the email address or phone number that you've designated as your primary contact point or as the contact point for the service involved.
Check the "Spam" or "Trash" folders in your email if can't find the email from Yahoo! in the Inbox. Sometimes non-Yahoo! systems incorrectly mark Yahoo! communications as spam; or you might have accidentally deleted the email.
Open the text messages area on your mobile phone or other communications device and locate the text message from Yahoo! if you're in the process of setting up a Yahoo! service for your mobile device or requested that Yahoo! send a confirmation code via text message.