Fix Duplicate Appointments in Classic Outlook Calendar

  1. Change the view on the calendar to List.
  2. Right click anywhere on the top header and select View Settings.
  3. In the Advanced View Settings List, select Columns...
  4. Add the Created and Modified time stamp.
  5. Sort by modified date. Look for the time the duplicates were created. Shift select all the duplicates at the time they were mistakenly created and remove them.