Misspianopants

My fiancé has his masters degree in education. He is very smart and a dear man but he mispronounces the word “accentuate” ALL the time. It’s a word he says often. He pronounces it “extenuate”. I should have said something the first time but now it’s been going in a year and I don’t know how to fix it! At first I thought maybe I was saying it wrong so I didn’t question it. How do I correct him so he doesn’t sound stupid in front of people?!