You will need a spray bottle that holds at least 500 ml. Put 500 ml of distilled water into the bottle and add 5 ml of 22.4% sodium chlorite. Spray that on the area and let it air dry.
This can be used 3 - 4 times a day, for about a week. Then you need to reduce the concentration in half.
Caution: Under certain conditions, this solution is strong enough to cause the bleaching of some fabrics.