Please avoid washing with water as much as possible. If you absolutely must wash by hand, use lukewarm water with an appropriate amount of mild detergent.
(Silk is a natural protein, and chlorine bleach will damage the fabric, so avoid using fabric softeners or bleach and wash with a silk-specific/neutral detergent.)
Wash by pressing or shaking in lukewarm water at about 30°C. Do not scrub hard or rub.
Wet the stained area and then use a dry towel to absorb the dirt along with the moisture.
Please be careful not to blur the surrounding area with a tightly wrung towel at the end, as this will result in a ring stain (a round stain with a border).