How do I clean up the CSI Assignee list?

We have active assignees in our "assign to" section of the CSI reminders screen for MILES!! We'd like to get rid of all the employees who no longer work with us to create efficiencies when we're assigning these CSI reminders. We've already cleaned up and inactivated people as "workers", but that didn't seem to have any effect in the CSI reminders screen. Help?!?