Hello! Had to change my newborn’s milk twice! You have to mix the formula. Something like this. 😃 hope this helps. It will be a gradual shift. It’s trial and error though. Similac total comfort didn’t work, nan optipro also didn’t work. We ended up with nan supremepro which is more expensive, but baby was born with tummy issues so we had no choice! If baby is healthy, can try one of the cheaper brands. I didn’t have much BM too, and FM is really expensive esp as they consume more. Hope this helps! All the best mumma ♥️