In order to unpublish a lesson you will need to first open the course the lesson is located in. Click on Student Work > choose the module & lesson you want to unpublish > gear drop down menu > Unpublish.
If any of your students have already started and/or completed the lesson, it’s IMPORTANT to know that you will not be able to see any of their work after you unpublish that lesson. If you republish that lesson in the future, your students work will be recovered.
In order to check if you have successfully unpublished the lesson, click on the Lessons tab (within the same course), search for that lesson and there should no longer be a published icon (blue book) to the right of the lesson. See below image:
If this does not solve your issue, please fill out the technical support form located here