How to get over gag reflex?

Sorry if this is the wrong sub to ask but how do you get over a gag reflex?I know some people don't have one, and others only slight ones that are easy to get over, but mine has always been super strong. Like, my dentist has to be careful when he is working in my mouth, sensitive.I've been dating this guy for several months and we haven't yet, but will eventually have sex for the first time. At some point, he will be in my mouth. How do I work on getting over it without just like sticking my fingers in there and throwing up?