I squirt just a little dish soap (Dawn) on the spot and, with a Q-tip, rub it in. Let sit a few minutes, then a take a toothbrush and work it til sudsy... Then rinse out with cold water using washcloth (finger inside so it doesn't touch other fabric). Works for me....Hopefully, you'll get it out...
i always empty the water out of my iron after everyday use to avoid rust developing... You'll need to run a mis water and vinegar through the iron to clean it out, possibly. Not sure, tho...