What is your Moodle version?
Based on the info you have provided it sounds like you just need to go the the "Categories and Items" view, select the edit icon for the course category and add an idnumber.
What is your Moodle version?
Based on the info you have provided it sounds like you just need to go the the "Categories and Items" view, select the edit icon for the course category and add an idnumber.