To renew or extend a course licence, simply purchase additional course licences. Once the driver's course licence has expired, go to Course and driver options > Add driver(s) using a form. Choose Existing driver. Begin typing their email or username. Add them to the course. They will retain any module scores from modules that they have completed in the last 12 months. The new course licence will give them full access to the course again for the prescribed period (usually 6 months or 12 months, depending on the course) 

In the image below, the company has 2 course licences expiring in the next 30 days.

You can click on the number use the Course and driver options menu