I would dust him with a good poultry dust (sevin dust works great) and put him on a good feed that is at least 20% protein and also has animal proteins in it.I have only just bought him and the people i got him of had another dominant rooster that wouldn't let this one eat so they have had to feed him separately but that doesn't help nearly as much as him getting his own food, that's why he is slightly under weight. I'm feeding him layer pellets at the moment is this alright or is it only for hes, i give the flock including him layer pellets dry and layer pellets soaked in water over night. Also he gets food scraps from the kitchen and our neighbors kitchens and they all free range for about 8hrs a day and it's summer where i am right now so plenty of insects and grass about. He was last wormed about 1 month ago but only one hen had the worms but i just gave the whole flock it.
I myself don't feed a layer feed to any of my bird, you would be better off feeding a good Starter Feed and offering Oyster Shells on the side.
Chris