Successful people still get nervous before big moments. They just stopped waiting for the nerves to leave first.

Nerves do not get trained out of anybody; experienced people have simply stopped treating them as a reason to wait. The feeling before something important is not a warning that you are unready, it is what caring about an outcome does to a body. People who perform regularly learned to begin while it was still happening. The difference is not calm, it is going anyway.

Before the next thing you dread, notice the symptoms without arguing with them. Then start on time regardless. Nerves usually settle a minute or two into the task, which you can only find out by starting while they are still there.