Since it's properties are similar to cotton, it is best to wash it in cool water. Lay it flat to dry, or hang dry. You will be happier with the way it looks after washing when you also iron it when it's dry.
Turn the garment inside out and wash by hand or on the gentle cycle of a machine with regular detergent. Hang to dry and iron if needed to regain finish.
Modal fabric is colorfast if you wash it in warm water. This means it can be washed in a machine washer like normal fabric. It should be ironed after after it is washed also.
Please use caution with this material. Hand wash or machine wash in cold water on the delicate cycle. Put in the dryer on cool, or lay out flat to dry.