When my chicken is sick the first thing I do is remove it from the coop. When you have a sick chicken the other hens will start to be mean to it so you need to get it out of the coop. You need to have a medium size dog crate or wire cage to have on hand, put the sick chicken in the cage and give it some water with a little vinegar.
Sometimes the best thing you can do is not feed it for a couple days or give it some wet bread. After it gets some strength back you can give it some regular chicken food. Then keep an eye on it and let it get it’s strength back before you put t back in with the other chickens.