What do you do if it has become a stain on the tie?
If you must wash the tie, go to a dry cleaning with experience of washing neckties. A necktie is washed like any other garment in the dry cleaner and it can lose form and luster and have rounded corners when it comes out of the laundry.
A recommendation is to never wash a quality necktie! If you would get stains on the necktie you can first try with a little bit with a stain remover on the back of the tie.