Best answer by Maryam
I think you can just resubmit your assignments and retake the quizzes to change the previous grades and performance. Have you tried it?
You can also unenroll from the course and re-enroll again, but this is an option that may have unwanted consequences. So, I would suggest that you consult the Help Center first. You have enrolled 2 years ago. The same enrollment options might not be available now.
(Edited by @Laura to add Help Center link.)