Talk to yourself as much as possible (without looking like a weirdo ofc), practice as much as you can on parts of speech you struggle with, practice your future stories and conversations you’re going to have, practice being that calm and casual with these certain topics, and then transfer all that to real conversations with people, the main thing you’re trying to transfer is the level of calmness, and casualness you feel when you’re by yourself just chilling. A lot of stuttering happens when you’re worked up either in an excited or stressed way, most of the times you don’t notice it. That’s why you don’t stutter by yourself, so take advantage of it.