He sounds like he has a respiratory disease with the cough or sneeze, congestion, and it looks like his right eyelid is swollen with eye drainage. Any bacteria, virus, or fungal respiratory disease can cause yellow or whitish plaques inside the trachea. But I think that it could be a foreign body, a piece of food, or possibly a growth as well. Hopefully the Tylan will help. Tylan dosage is around 12 mg per pound given 3 times a day. You can give injectable Tylan orally, by the way, especially since the injectable can cause muscle necrosis at the injection site. There is also tylosin powder that cannbe used in the drinking water available here:
https://www.jedds.com/shop/tylan-soluble-100-g/
Does he have a bad odor coming from his beak? Can you look inside his beak with a flashlight while someone holds his head still for any cankers or tissue that should not be there?