ok.... vibrato is a natural thing that just happens when you sing. Its how your body deals with the stress. Even though it is natural, some people force it, which not only doesn't sound good but its unhealthy. So first relax, then if you still have too much vibrato, hold out a note on Oh, without vibrato, and then slowly increase your vibrato (not volume). Singing with out vibrato is just as stressful on your vocal cords as forcing vibrato, so relax, and don't over sing. Hope this helps.
