Was the fabric 100% cotton?
Did it have a "painted on" print design?
Did anything on the yellow fabric smear or melt when you put the iron on it?
Try a scrap and hit it with the iron...does it do the same thing?
Use this scrap after you get "silver" on it to work on different techniques to get it out. Do not use your project.
Try placing a 100% dish towel over the yellow scrap, no steam to see id the silver will left off onto the dish towel.
Then try washing the scrap to see id the residue will come out.
Take the project ans scrap to your local dry cleaner. They may have an answer since they deal with all types of fabric.