Ask for advice: do you already have a doctorate in China and can you go to New Zealand to study for a doctorate? Will you refuse a visa and think it is a serious immigration tendency?

There is no problem when applying. The school will only examine your intention and whether your professional qualifications are up to standard.

If it is stated in your application that although you have a doctorate, you still want to study different majors, then it is ok. As long as the reasons are sufficient and the conditions are qualified, you will pass.