This can only happen in one of two ways:

  1. You've deleted a driver that has accepted their course licence
  2. The course licence has expired and wasn't renewed if it was a renewable course

In either case, you will need to purchase a new course licence to replace the licence that was deleted or expired.

If you accidentally deleted a driver that had started a course, unfortunately, this cannot be undone. If you deleted a driver that hadn't started a course, the course licence would have been added back to your spare licences.