Cross-listing allows you to move section enrollments from individual courses and combine them into one course. This feature is helpful for instructors who teach several sections of the same course and only want to manage course data in one location.
How to do it?
1. Get to the course you want to cross-list
Navigate to your courses in canvas and select the course you want to cross-list or "child course." In this context you are going to have a "parent course" which is the one that will have all the content (All the assignments, Quizzes, homework, etc.) and "child" courses which are the ones that will get cross-listed, meaning will get all that information from the parent course.

2. Select a section to cross list
Once inside the course you want to use the right side menu to go to course settings (3) and from there we want to go to sections (4) here we will find all the sections associated with the course and we will also see if an already existing section is already cross-listed or not, and to what course are they cross-listed to. Here select the section you want to cross-list by clicking on it (5).

Notice:
1) You can view a cross-listed course's originating course when course sections are cross-listed.
3. Cross-Listing
Once inside the section settings, there is an option on the right side of the screen saying "re-cross list this section" (6) when you click on it a pop up menu appears. From here use the search bar (7) to find the course you want to serve as the home course. Then click on "Cross-list this section" to do it.
Warning: You will loose access to the original section and it will not be available in the dashboard anymore. To de-cross list follow the instructions in the next section.

How to undo it?
De-cross-listing is an action that is not available for faculty and staff. However the way to go about it would be submitting a ticket to canvas help. In the side bar navigate to the help menu (1) and click on report a problem (2).

Once here give your ticket a subject (3) in this case "de-cross list a course". Then give it a description (4) you should put the name of the courses you want to de-cross-list along with an easy way to find it such as a link. In "How is this affecting you" (5) select appropriately to how its affecting you in your class. Finally submit your ticket (6). You should hear back from canvas once it is done.