The following article goes over how to reset your AX account password on password.ucsd.edu.
If Duo is telling you that you do not have access, please sign up for Duo at duo.ucsd.edu. You can follow the instructions on Register for Duo Two Step.
If you still have questions or need additional assistance, please contact the ITS Service Desk. You can call us at (858) 246-4357, email us at support@ucsd.edu, or submit a ticket at support.ucsd.edu.