You should NOT iron a silk tie.
Many high quality silk ties are manufactured with rolled edges that give the tie a fuller more supple appearance. Ironing the tie, or having it professionally dry cleaned and pressed, will flatten out the edges and change the look of the tie.
How to Get Wrinkles Out of a Silk Tie
If you can't iron a silk tie, how are you going to remove those wrinkles and bring it back to its original pristine shape? The best way is to use a hand garment steamer. Hand garment steamers can gently remove wrinkles without pressing and should be performed systematically every few months.
If You Must Iron Your Silk Tie
If you don't mind the change in appearance that ironing will bring to your tie, you can iron it carefully as you would any other delicate silk garment. Setting your iron on a low heat setting, place your tie right-side down between the fabric covered ironing board and cotton fabric. Iron the tie through the fabric, ensuring that the silk tie never meets with the iron directly.