You can manually retrigger credits for a student by changing their grade to a 0 and then adding their original grade back in.

To do this for students in a specific course:
  1. Go to Academics > Grades > Grading Setup > School year setup
  2. Select the Course Grade Plan Group from the available drop down 
  3. Click View for the appropriate Grade Plan
  4. Extend the Review End Date to open up Grading Review
  5. Go to Approval > Grading - that should be the only grade plan open
  6. Search for the course and click Review
  7. Take a screenshot or make a note of all students and their grades
  8. Change each grade to an F (this causes the trigger to occur and remove the old earned credit)
  9. Click Save
  10. Put all the correct grades back and click Save