Dear Teacher/Professor/... X,
I am writing to inform you that I am struggling with SUBJECT A, I would like to request a seminar class to dicuss about ... to improve notions about this subject
The issue is that (Chỉ ra vấn đề).
With your approval, I (could attend your class, or having a lecture...)
Thank you for considering my request and I would be happy to come in and discuss the matter further.