More than likely, you won't be able to do anything to correct the old lense. The most common way that I know of to fix the problem is to take a piece of clear plastic that is slightly larger than the old unit, rough shape it, glue it in place and then carefully file and then sand it to shape (using progressivly finer sandpaper), Finish it by polishing and cover w/future.The light bulb inside can be represented by drilling a small, shallow hole on one of the inside faces of the piece and then carefully adding a small drop of the proper colored pain to the hole.
I've found this method to also work very well for landing lights located in the wing leading edges. I enlarge the hole in the wing slightly and add a piece of clear plastic that is some what larger than the origional part, then go thru the file, sand & polish routine. This gives me a clear piece with no gaps to fill and when I'm ready to paint, I simply apply a piece of tape cut to the size and shape of the clear lens and them paint.
Hope this helps a little