Although many instruction suggest silk yarn clothing can only be dry washed. If following some tips it also can be hand washed.

Silk yarn clothing should be washed with specially formulated detergent or mild shampoo.
Put your silk yarn clothing in luke warm water and soak for 3 to 5 minutes. If your silk yarn clothing is dark-colored or printed do not soak it and wash it quickly in cold water;
Move the silk yarn clothing from side to side, do not wring or twist it;
Silk yarn clothing is very delicate so handle it with great care.
Remove your silk yarn clothing out of water after 5 minutes. Rinse it several times with clean water and add some vinegar to get rid of soap completely.
Wrap the silk yarn clothing in a clean towel to remove the excessive water. Change several dry towel if need.
Roll out the silk yarn clothing and straighten it gently at the corners

Iron it. Set the low setting to iron it.
Silk yarn product should always be ironed from the backside.

It should always still be slightly moist.

Don't iron silk yarn product too hot!

Always remember that silk yarn clothing is a protein structure much like human hair. Heat will damage it.