The same way you organize anything. Start by talking to a couple trusted coworkers to form an organizing committee. All the members of the OC need to talk to coworkers, handle workplace drama, agitate for better conditions, educate people about unions, maintain systematic campaign tracking, and fight against the boss during their union busting campaign. When I worked remotely, it was as simple as sending a dm like this:

Hey, would you be able to talk over break? Some coworkers and I were discussing some issues and I wanted to hear your thoughts.