First Time BJ

okay, I need help. An abusive ex that stole my virginity tried to force me to go down on him, so I bit his junk. Anyway, I'm in a happy committed relationship now, and he wants a blow job and I want to be able to do that for his upcoming birthday. After what happened I have such anxiety about it, plus I've never actually given one so I don't have a clue what to do. any advice on how to get past anxiety and/or actual techniques for when the time comes?