Hi Liz

There is a script that may be able to be used that will delete all (or a time-based subset of) unstarted course completion records of users who are no longer enrolled on a given course. This script can be found at admin/cli/delete_unused_course_completions.php and can be run with a --help flag to output usage instructions.

When run, this script will log that it has executed, and include the parameters used as well as how many unstarted completion records were deleted.

It is important to back up the database before you run the script. 

The users will need to be unenrolled from the course - how were the users enrolled ? If they were enrolled in the course by audience then this should be able to be done through the audience. if manually enrolled then each user will need to be manually unenrolled.

For the second question on the Not tracked can you go to the course and select Edit settings and check that enable completion is set to 'Yes'

regards