First pin the skinny part of the tie to the thick part.
Fold the tie as many times as you want. Pin each fold down.
Go back and tack each fold. (This means to loosely sew them down.) Try not to let the tread show on the top part of the tie.
Make sure you can slip the necklace on and off over your head. You should add a or take away folds to make the fit better.
Sew the skinny end and the thick end together.
Sew on the button.
It should look something like this.