I was heartbroken when by favorite cashmere sweater showed up in my clean laundry basket, looking a bit miniature after a spin through the washing machine!! Was relieved to find this bit of advice on how to un-shrink a sweater:
Fill your sink with warm water, add a tbsp of hair conditioner. Submerge the sweater and let it soak for half an hour. Then gingerly tease the fibers apart – this can be time consuming and tedious – but it works! Once you have teased out the fibers, gently stretch out the wool in all directions. Finish with a cold water rinse and lay out flat to dry. You should gain a few inches.