The first step in successfully removing pen whitener stains from clothes is to gently rub the affected area with a clean cloth to absorb the extra liquid. Do not rub as this may cause the discoloration to spread. Next, immediately apply a tiny amount of liquid laundry detergent to the stain and rub it in carefully. After letting it sit briefly, wash the clothing in cold water.

Before the stain dries, check it; if the stain still exists, try again or use a stain remover made especially for stubborn stains or ink. It is important to follow the care label recommendations on the garment and avoid applying heat until the stain has entirely disappeared, as this can increase the colour. Pen whitener stains on clothing may be removed by consulting with a professional cleaner for very difficult stains.

Original Source: https://www.quora.com/How-do-I-get-rid-of-pen-whitener-stains-from-clothes/answer/Hello-Laundry