Google - hello I have a new holland tm120 tractor it doesnt go reverse can any one help me fix it ?

"doesnt go reverse" might mean that you can't physically move the gear shift into the reverse position, or that you can but the gears don't mesh, or that they do but the engine dies, or several other things. It is unlikely that anybody hanging out here will know enough to guess which you meant. The best thing to do is to find a mechanic who can look and see what's wrong and fix it.