Appeal deadline questions after an unemployment denial after 9 years as an electrician's helper

I got a denial letter last week saying I left my job voluntarily, but I was let go as an electrician's helper. It has been weighing on me all week. I have not done a hearing before and I am nervous. If you have appealed before, what helped you prepare?

Thanks for writing this out. I went through something close to it 3 months ago, and it got easier once I kept a simple log of every call and form.