Denied unemployment, how do I appeal? (Boston)

I got a denial letter last week saying I left my job voluntarily, but I was let go as a dental hygienist. I am in Boston, in case local advice matters. My employer's version of events does not match mine, and I have emails that show it. If you have appealed before, what helped you prepare?

Stay calm and stick to facts. Mine lasted about thirty minutes and felt more like a conversation than a trial.

I printed my emails in order and wrote a one-page timeline. The hearing officer kept going back to it.