Changing lever does not work ford Tran 350L

Hello forum, my Ford Transit 350 l van I have taken it out of the warehouse, I will make
several maneuvers and suddenly the change lever is blocked without being able to put it in any position is currently in the senguce march. What can happen to you thanks

If the thing is that you cannot move the lever to get the march (with the engine stopped) I think that you can have a problem in the blacker that goes from the lever to the change and you will have to get underneath to see what there are, if you have released any label of the levers or if the adjustment screw of the control bar is lazy, another thing is that you cannot change the march. The engine stopped to get an idea and be able to help you. Greetings!!