Hello there, @melizabethfinne Welcome to the Canvas Community. Thank you for posting your question. Please check out this Guide: How do I de-cross-list a section in a course as an instructor?. You need to be logged in to the course where all the enrollments are at for both courses that you had cross-listed. Cross-listing courses moves enrollments from one course to another, and that's why you cannot get to the original course at the moment.
I hope this helps, Mary. Sing out if you have any questions. Take care...stay safe...be well.