If you want to place a grass texture
on top of the plateau (like the hanging islands in SkysRim) then a new UV map is required since we don't know the current one for the plateau. Blender probably the easiest way to make a new UV map unfortunately, along with re-exporting the mesh with the UV map. I will happily re-export and make a new UV map for you to draw over.
Once you've made the new image then all you need to do is go to the link Lord Suragaha has posted
