Do I need to fill out a health certificate to go to Tibet by train now? Where can I fill it out? Urgent = urgent = urgent = urgent

It's not a health certificate, it's something like a statement. In fact, it is to make sure that you can adapt to the plateau environment, which is a kind of shirking responsibility.

I may give it to you when I buy the ticket, or I will give it to you when I get on the train.

You don't need a hospital. If you are worried about your health, you can go to the hospital for a physical examination.