Start now, and decide to be on the alert for moments in which you use the most obvious throat-clearing language, the stuff that lets imposter syndrome undermine your footing on the things you know that you know:
“I think that…”
“I believe that…”
“In my opinion,…”
“I just wanted to…”
“Actually,…”
For a day, maybe more, play around with eliminating these in your writing. Instead of “just wanting to ask about XYZ,” come right out and ask about XYZ. Don’t buffer your real question, and (harder still) definitely don’t buffer your real statements with “I think that” and “Maybe it’s best that” and other word-bumpers. Just say the thing.