Chlorine, or Javel, is a bleach often used in cleaning. A small drop is enough to leave white stains on your clothes or fabrics.
In many cases you can touch up light stains with bleach fairly well. However, if the chlorine gets on the fabric undiluted, the fabric itself may be damaged. Chlorine can even cause holes in the fabric that often only become visible after a wash.
When correcting stains, the first step is to dissolve a little bit (a pinch is enough) of fabric dye in 10 cl of water with a little salt and vinegar if necessary. You can touch and rinse the stain several times with a cotton swab.
There are millions of colors, so finding exactly the right color is difficult. However, if you start with a slightly lighter color tone, you can always make the color slightly darker, warmer or cooler from there.
It takes some feeling for color mixing and experimentation, but usually it is quite possible to get very close to the original color. To make the color tone warmer or cooler, you can use fabric dye in the primary colors red, yellow or blue. Brown and black are great for making the colors darker.
When looking for the right color, it is important to work from light to dark. Darkening a light color is easier than the other way around.
If you have found a reasonably good result after tapping and rinsing, the last step is to dye the entire garment again with the correct color. This makes the end result uniform in color again.