the way to bring back the milk supply is the same as the normal way to increase milk supply..
you can try to latch baby as much as possible.. if you still have little milk, let baby latch each milk time (2hrly) be4 you give him the formula milk .
if you have the time, you can try power pumping.. means you pump like 15 mins on each breast, every hourly..
hot shower/massage on breast..
drink plenty of hot fluid, green papaya fish soup, red date tea n stuffs like that..
you can also try domperidone n fenugreek...
check out other thread on ways to increase supply as well..