...
- Login to the tenant as the tenant admin
Click the HOME link in the upper right corner of the page. See the image below.
- Click the Tasks tab
- Click the search icon
To Abort a task pending for a specific user:
- Select Joe's the username from the Locked By User dropdown
- Submit the search form
...
The only user that has the permission to actually delete completed tasks -- those in the Submitted or Aborted state -- is the form/flow's designer. See viewing and managing submissions.