Got a denial letter for unemployment, what now? after 13 years as a software tester

I got a denial letter last week saying I left my job voluntarily, but I was let go as a software tester. I do not usually post, so bear with me. I have not done a hearing before and I am nervous. If you have appealed before, what helped you prepare?

File the appeal before the deadline, even if you are unsure. You can gather documents afterwards. That is the one part I would not wait on.