First, you must thaw the milk by moving it from the freezer and into the refrigerator. Thawing can take up to12 to 24 hours so you should remove it from the freezer early enough. Once thawed, you can put it in a bottle for the baby to use and keep the rest in the fridge. The best way to heat the thawed milk is by using a bottle warmer or running under warm water. It is, however, important to note that thawed milk should never be refrozen. It can keep for up to 24 hours in the fridge so if your baby does not consume it all within 24 hours, you should simply discard it.