/u/flip69 has made a great write up on the subject that is very thorough, and can be found here

https://www.reddit.com/r/Chameleons/comments/1dndbr/veiled_with_an_advanced_lung_infection_signs_and/

The chameleon's lungs fill with mucus. This results in billowing breaths and possible crackles when breathing. There is a very unique posture where the head is tilted upward and the tongue is distended in the chin. Labored breathing is usually the first symptom.

Treatment is Baytril. I administer through a 1 mL needleless syringe. I fill a drop of baytril into the syringe, then fill the rest of the syringe with water. I drop into the chams mouth. Allow the cham to swallow in between each drop given. Give 2-3 times daily until symptoms stop.

Baytril is very harsh stuff and tastes terrible. The chams don't enjoy it. Don't over medicate.

If working with a small hatchling that is a few grams or less. It is very difficult to give a small enough dose without killing the cham. As tiny of a drop as possible should be given. But even that is likely too much.