★★★★★
After a lot of trial and error, here are the supplements/ food that helped him tremendously.
Ancestral trachea beef supplement (amazon), organic canned pumpkin (2 tablespoons daily), Curly Parsley (1 teaspoon daily). Ground eggshell (half teaspoon daily), No kibble. This makes the condition worse. Steamed chicken or beef with veggies is what they have to eat. And lastly, do not crate them, they need to walk around freely because it prevents the anxiety which is a side effect of this condition due to insufficient oxygen because of the collapsed trachea. If you have to crate them, make sure there's a doggie door so they can come out if they want to.
Side note, since implementing the above, my sister's dog is almost normal again with barely any coughing. Not saying this would work for every dog but it's what worked for us and I wanted to share even if it helps just one dog.