Ignoring the fact that you can just pick the lock to get in the cab, there is a mechanical override on the airbrakes for just this sort of problem, every trucker and tow operator knows this. Each air brake cylinder has a caging bolt, spin that in and it free the brakes, all you need is a 3/4" wrench

https://www.youtube.com/watch?v=dwmt3zuRoYA

You could go do this yourself right now and cause a whole lot of trouble