How do you heal a sick parakeet?

Take him or her to a vet immediately. Do not use antibiotics for sale at pet stores; you have no way of knowing if the problem is caused by a respiratory or digestive infection, liver disease, or one of any number of avian diseases, each requiring different treatment. Take your bird to a vet! Until you get them their, keep them warm, possibly putting a light on the cage or a heating pad underneath half the cage. By keeping them warm their bodies can use calories to fight off disease rather than regulating body heat. Offer them millet, its easy to digest and be sure to put a shallow dish of water on the bottom of the cage in case they are not up to perching.

Best of Luck!