@JeffMonjack ...
I would agree with both @nwilson7 and @blopes on this one. I'll just throw this out...that if you were able to de-cross-list courses, you need to be logged in to the course where all the cross-listed courses were merged into. For example, sometimes people call this the "parent" course and then all additional courses to be cross-listed are the "child" courses. So, course "A" might be the "parent", and courses B, C, and D are the "child" courses. All courses are cross-listed into course "A" ... the "parent". So, you would need to log in to course "A", go to the "Settings" page, then click on the "Sections" tab. Next, click on the name of one of the "child" courses ... B, C, or D. Then, you might have the option to de-cross-list. Again, @nwilson7 and @blopes have given you great direction on what to do if you still do not have this option available. Hope this helps in some way.
How do I de-cross-list a section in a course as an instructor?