The best course is to take it to a bike shop and have them align your derailer hanger. Short of that, you can try bending it back into place. Whatever you do, do not grab the derailer cage and pull. Insert an allen wrench into spot where the derailer bolts on to the hanger and use that for leverage to reposition the hanger. It won't be perfect, but you should be able to get it pretty close with this technique.