You ought to have a brake cable looking similar to what you'd find on a dirt bike, but much longer running from the park brake peddle down and under the coach to the rear axle. Before reaching the rear axle, it ought to Y off with a cable going to each hub. Within that Y connector, you should see an adjustment bolt or something similar. Pretty much straight forward on how it works once you find it. ...... Thinking of how long that cable will be, there also may be an adjustment nut under the dash where it connects to the applicator peddle.
You say that brake peddle goes to the floor with no resistance? I gotta wonder if the rear brakes are worn out. Maybe someone in the past drove that unit with the park brake set wiping out the rear brakes. You might also have a broken brake cable. I've seen quite few give up the ghost right in the Y connection previously mentioned.
In any case, it shouldn't be anything you can't fix yourself. Even if it means new rear brake shoes and drums. Good lock with it!