Noob at oral..

I’m currently with a man I love so much and can actually see myself marrying and the sex is great but the one problem is I don’t give him oral.. he says he is ok with it and it isn’t something he needs yet every time we are in the middle of sex he asks me if I could just go down on him for a second and it always ruins the mood. It’s not that I don’t want to it’s that I never have before and am super nervous about how terrible I am going to be at it. Does anyone have any tips on how to make me less nervous?