ok so here are a few things that will help you but for some you have to stay committed
take your tooth brush and scrub in circles starting at the tip of your tongue and work your way slowly to the back until you find the spot that makes you gag, then brush in circles over that spot for ten seconds or until you cant anymore doing this everyday will slowly but surely desensitize your gag reflex when you conquer that spot move the toothbrush further back and continue till you are satisfied my other tip which is quite helpful spray chloroseptic in the back of your throat about a min before you go down its an oral anesthetic and will numb the area