There are many customs declaration schools in Dalian with different teaching levels, but most of them are based on book knowledge.
Moreover, customs declaration and inspection is a very practical work, which is very different from books.
If you want to engage in this industry, research is necessary, but practice is also essential. But you don't have to go to customs declaration school.
I think it is ideal if you can directly find a job with a freight forwarding company (don't worry about salary first), and after you are familiar with this industry, you can study customs declaration while working and take exams. Of course, it's difficult, because you can't be a customs broker without a customs declaration card, but you can do the most basic work of running bills and learn a lot from it.
Or study online first. There are many websites on the Internet for the examination of customs declarers (there will be many if you search). Their knowledge is comprehensive and timely, but you can communicate with others more and improve quickly. Of course, I suggest you buy books for the customs declaration exam. Xinhua Bookstore sells them.
No matter through what channels you get the customs declaration and inspection certificate, it mainly depends on your personal efforts. I wish you an early success!