Denied unemployment, how do I appeal? after 12 years as a welding apprentice

I got a denial letter last week saying I left my job voluntarily, but I was let go as a welding apprentice. This is my first time dealing with any of this. I have not done a hearing before and I am nervous. If you have appealed before, what helped you prepare?

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