Nervousness in trading could come from rational concern and irrational one.
Mine was irrational. My way to tackle it now is through music listening. However, instead of listening to the typical calming instrumental musics, I listen to upbeat, happy-go-lucky kind of music.
The reasoning is this. If you go with the calming one, it's like you're trying block and downspeed a strong river flow with just a few rocks. It'll be very unlikely for you to be successful with that. Your rushing stress hormones, i.e. adrenaline and cortisol, just won't be tamed so easily that way. If you have tried that, you know what I'm talking about.
Hence, I suggest we go with the other option in which we won't try to block it but try to ride and have fun with it. So what this do is trying to change stressful hormones to happy hormones, be it endorphins, dopamine or serotonin. The first one was trying to change stressful hormones to empty, emotionless feeling. Which one do you think would be more fruitful for you?
Now comes to technicality. It's simple really. Here's my favorite upbeat, happy-go-lucky Playlist produced by Alumo. When I feel nervous or other negative feelings, I just listen to them and put a smile on my face. I don't have to force my feeling to be happy, calm and content. I will feel those eventually pretty quickly while listening to the musics.
So hope that helps for ones who have irrational nervousness. If you have a rational one, start by tackling the problems first, then go with this approach.