If your organization has scheduled an interview using the Outlook 365 integration, you can cancel/delete the the interview directly from Greenhouse Recruiting.
Navigate to a candidate profile with an interview that needs to be cancelled (All Jobs> Job >Candidates). From the candidate profile, navigate to the Stage tab on the On Job panel and expand the stage that requires a cancelled interview.
Click Update next to the scheduled interview.
Navigate down the Schedule Interview page and click Delete Interview.