I usually dip their beaks into water to get them drinking on their own. You can tube feed larger amounts of fluids and some KayTee Exact baby bird feed. Hear in post 2 is some info on giving a small amount of fluid:
https://www.backyardchickens.com/th...fulids-with-syringe-for-sick-chicken.1436803/
https://www.backyardchickens.com/th...fulids-with-syringe-for-sick-chicken.1436803/