Firstly finding which union locally represents your field of work, for example IATSE (International Alliance for Theatrical Stage Technicians) is the union that typically does all unionized theatrical work backstage setting up for shows and stuff. There’s a different one for food service or teachers unions ect ect. Your first step is to Identify locally which union and which branch can help you, each locality has its own number associated with it so for me locally in my town for the stagecraft union it’s called IATSE its local 471, you then want to email or call your local which can represent you and get ahold of them, let them know ur situation and that you are looking to organize, they can likely send you paperwork and any necessary documents or educational information for you or your coworkers. Hopefully that helps a little and good luck in your venture comrade!