Chickens dont need baths ussaly! only if they have a cut beak(then they cant clean themselves properly) they just dont clean their feathers or they have a messy but or other health condition. I a chicken has white Feathers and they get messy you can give them a bath Heres How:
Step 1: Fill your sink or a dish tub with warm water
Step 2: put the chook in the tub and make sure she stays there( this could be a 2 person job)
Step 3: use dawn or baby shampoo on the feathers
Step 4: rinse
Step 5: this part seems odd but chooks love it BLOW DRY THEM!
Step 6: give he/she some treats
between step 5 and 6 your hen should love you again!!!