Canceling an active lease will need to be done offline and not through Zillow. Active leases are unable to be deleted or canceled.
If you need to delete a lease draft, you can do so by logging into your Zillow Rental Manager, selecting the Manage tenants tab, then selecting View all leases. From this page, simply select the ... button and you will see the option to delete your draft.
If you have additional questions about how to terminate a lease, please contact a local legal professional.