The problem of Australian study visa not being issued on the start date of school

Huh? Your question is very confusing, and you don't explain your current situation clearly. Let me give you a rough outline.

If you are in Australia, there is nothing to worry about. As long as the visa application materials are submitted before the visa expires, you will have already obtained the bridging visa on the same day. The bridging visa is a temporary visa. You are on the bridging visa until your next student visa is signed. The visa requirements are the same as the student visa.

If you are in China, yes, you need to change to the next enrollment date (if it is a direct university course, the next semester will start in July). If you have paid your tuition and the school has given you a CoE, you need to find the school to extend the CoE until the next semester. If your original CoE was from April this year to December next year, it will now be changed from July to March next year. The visa time is based on the length of your course, and the length of the course will naturally be longer.