Denied unemployment, how do I appeal? - 4 weeks in

I got a denial letter last week saying I left my job voluntarily, but I was let go as an accounts payable clerk. This is my first time dealing with any of this. 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.