Hi Jinyi,

Thanks for your question.
Is this a public course? If so, you can leave the wrong class and join again to enter the correct one.

https://help.openlearning.com/t/h4p5fj/how-do-i-leave-a-course

If it's a private course, it would be best to contact the course staff. You can post a comment within the course or send them a chat message if they have chat enabled.