With minimal correction:

The course I want to take is Miss Wang’s badminton course. She was an athlete. She retired from the national badminton team and now she is my college teacher. I have been in her class before. I think she is the best badminton teacher in my college. But unfortunately, she is not eligible to launch a course because of new rules which say that teachers who want to launch courses should have their own published papers. Miss Wang focuses on real sports; so, she doesn’t have her own paper. I want to take her course because she has a great training method which helps us improve. She has advanced and professional theories. We can improve our skills after learning from her.

With additional suggested edits:

The course I would like to take is Miss Wang’s badminton course. Miss Wang was an athlete who retired from the national badminton team and is now my college teacher. I have been in her class and I think she is the best badminton teacher in my school. Unfortunately, however, she is no longer eligible to convene a course because of a new set of rules, which states that teachers who want to convene a course need to have published a paper. Miss Wang has always prioritised practice over theory; so, she has yet to publish an academic paper. I want to take her course because she has a great training method, which I believe is capable of helping me improve. Despite not having published her own paper, Miss Wang’s theoretical understanding is solid – and she is very capable at applying theories to practice. I’m confident that I will be able to improve my skills under her guidance.

Note: There is a contradiction in the paragraph. You said: Ms Wang is not eligible to launch a course. But she has a course (which you wish to take). So, this needs to be clarified.

Aside from this, your English is very good. Well done.

A course I want to take

Could you help me correct my mistakes？thanks！

The course I want to take is Miss Wang’s badminton course. She was an athlete. She retired from the national badminton team and now she is my college’s teacher a teacher at my college. I have been in her class before. I think she is the best badminton teacher in my college. But However, unfortunately she was not an eligible teacher to launch course because of the new rules which said say/state that teachers who want to launch courses should have their own published paper. Miss Wang focuses on real sports so she doesn’t have her own paper. I want to take her course because she has the a great training method to that will help us improve. She has the advanced and professional theory. We can heighten our technology techniques after learning from her.

'Published paper' - do you mean a newspaper? or documents?

'Real sports' - live sports?

Well done! Great work. I hope she is able to launch her own course soon :)

A course I want to take

Could you help me correct my mistakes？thanks！

The course that I want to take is Miss Wang’s badminton course. She was an athlete, who retired from the national badminton team. Now, she is my teacher. I have taken her class before. I think that she is the best badminton teacher at my college. Unfortunately, she did not have the credentials to launch a course because of the new rules. It states that teachers, who want to launch courses should have their own published papers. Miss Wang focuses on real sports, so she doesn’t have her own papers. I want to take her course because she has a great training method to help us improve. She has an advanced and professional theory to heighten our skills.

A course I want to take

Could you help me correct my mistakes？thanks！

The course I want to take is Miss Wang’s badminton course. She was an athlete. She retired from the National Badminton Team and now she is my college’s teacher. I have been in her class before. I think she is the best badminton teacher in my college. But unfortunately, she was not an eligible teacher to launch the course because of the new rules which said teachers who want to launch courses need to have their own published paper. Miss Wang focuses on real sports so she doesn’t have one. I want to take her course because she has a great training method to help us improve. She uses an advanced and professional theory. Through learning from her, we can improve our skill.