I find that I have a bit of stress when going to do stuff like tell people I don't know over the phone that I am trans and stuff, what I do that makes it a bit easier for me, is not to think about it. Like when I am dialing the number to the place I tend to just think about something else and when I start talking my mind is also elsewhere, but then once I start talking I am free to put my mind on the issue at hand, I can't chicken out once I am already talking to them, I would feel stupid then. It is always getting started that is my problem.
Just breathe, be calm, imagine the letter has different contents if it helps you and hand it to him is my advice. I am not sure if that helps, but it works for me. Good luck .Alexander!