When a course is marked "Completed", you will be prompted to certify each student. For each student, you can add interest in con-ed courses. By default, EVE will present the list of courses where the course being completed is a prerequisite.
Therefore if, as an example,  you wish to add the Wreck Diver Specialty course to that list, please proceed as follows:
Go to Data
Go to Course Type and click Find
Select a course you wish to add as interest and double click to open it
Select the General Tab
Set the prerequisite course
Click Save