If you are a Life or better NRA member, just hit the # on the menu for that class of member and ask about becoming an instructor. You will, at least I did, get someone in Training who will assist you. I call them about once a year for various reasons.
If not, hit the # for Training on the phone menu, but my experience is that you will have to leave a message and will get a call the next day or maybe one after that.
Pretty easy, though.
NRA Law Enforcement Instructor beginning in 1969, but, when I wanted to give that up in the 90s, I got the other ratings so I could continue to teach CCW Classes.
If you have an FDLE Firearms Instructor's card, you don't need the NRA, too.
But you must be a LEO or retired LEO to have that.
Bob