Bring chicken inside. Gently towel dry the worst of the moisture off of chicken. Leave in an area that is warm to you but not hot. Keep drafts away especially cool/cold ones but allow for fresh air to circulate around chicken.
If chicken's condition doesn't improve, wrap in warm towels and put in a warmer place. A blowdryer on a low setting will help to dry outer feathers. The finer feathers, down, and larger feathers at the base will take more time, maybe a day or two, to dry completely.
I'd keep your chicken in a warmish and draft-free area for a day or two. Feed regular food and supply warm water enriched with electrolytes per the serving directions. Keep in dry, comfortable bedding.
I had the same thing happen some time ago. She was absolutely motionless, floating in the pond. Cold. I thought she was dead, and when I scooped her out, also thought her movement was that reflex movement, not life. But she did it twice, so I rushed her inside.
I dried her with towels, pressing to get the most of the water out of her feathers and then used my hair drier to warm her. I'd set her down in a towel lined box with a light towel around her body, with a heat lamp over the box. Every few minutes, I'd pick her up and blow dry her some more.