I would isolate that chicken in a warm place. Maybe a crate or dog kennel or pet carrier. Make sure to keep it warm and give it food and water.
I have a vet that I consult but if you don't hopefully others will have ideas for you!
If you know the weight of your chicken maybe you could call your vet (do you have a dog or cat vet?) and they could give you some Baytril which is a good antibiotic for chickens. They could help you figure the dose if you know your chickens weight! Good luck!