Taking undergraduate course by a graduate student, officially?
No one can answer this question, except possibly your new supervisor. The bureaucratic issues involved in having a graduate student take an undergraduate course for credit, not to mention a course at another university, are very complicated and will be different at each institution.

(Before you spend any time trying to answer this question, you should check with your supervisor to make sure that they want you to take this course. For example, they might feel that despite the overlap in course material, taking this course would not be a good use of your time.)