Delete scheduled posts in bulk
If you wish to remove all scheduled posts from the list at once, you may do so from the Scheduled view.
Select all of the posts using the checkbox in the top-left corner and then click the trash can 
icon (to delete them).
- Click on the Scheduled view
- Scroll down to the last post
- Click the check box in the top-left corner
- Click the trash can icon to delete
Note: Depending on whether or not all of the scheduled posts have been imported into the list, you might need to repeat the above steps again.