You're in luck: creating a new class is easy in MindTap.
Go to www.cengage.com. Click on "sign in" to get to your instructor account. Once you are there, you should see the product you've been using. If you are still using that same textbook, then click on "Create Course" underneath it. You can copy your course from the previous semester. Then, you can make changes to dates, new assignments, organization, etc. And this new course will also have a new course ID for you to give your students so they can be sure to enroll in Spring 2019.
Good luck! Let us know if you need further assistance, and best wishes for a great upcoming semester.