You should cancel your Otago application through eVision. The process to do this will vary depending on what stage of the enrolment process your application is at.
If you have been offered a place in a particular programme (see your Alerts in eVision), declining the offer will cancel your application for that programme. Otherwise, go to the Programmes and papers section, select the relevant programme, and click the Cancel application link.
If you have selected papers, been course approved or are course declared then you will find information in the related answer:
Applying again in the future
If you haven't studied at Otago before and you choose to cancel your application, you will retain access to eVision with your current login details.