Tractors

I have a 20hp 48in riding tractor. Model number is PD20PH48ST. I cannot get the tractor to move forward or reverse. I get the tractor started, release the clutch and press the forward, or reverse, pedal and have no movement. Now I am not a mechanic but I believe the problem lies here: on the rear of the tractor there is a lever used to put the tractor in neutral if needed to push the tractor manualy. For some reason that lever is missing. I am assuming that was engaged before it went missing and now I cannot disengage it for the tractor to move under its own power. To add to the problem, I called and they no longer produce or even have a manual for this tractor so there is no help from them. So does anyone out there have an old manual or have an idea of how I can get this tractor moving forward? I thank you in advance for your help. Jake