To tackle your burn stain, you will need to grate some Marseille soap. “Mix the shavings with white vinegar (two tablespoons) and fine salt (two teaspoons).”
You will then place this mixture on the burn mark and let it work for a few minutes before rinsing thoroughly. Let the fabric dry and then inspect it. If the stain has not disappeared the first time, repeat the same process. However, if you do not have Marseille soap or white vinegar, you will find two other tips on La Belle Adresse, one with hydrogen peroxide, and the other with lemon juice.

Source :

“How to remove an iron burn mark?”, La Belle Adresse.