if it is just one or two, take a pair of finger nail clippers and clip a little of the top beak off (just a little) and that may stop it from pecking the others, i had one in the batch before this last one that i had to do it to as a last thing to try, for i had put the ones that were pecking in a 2nd brooder and he just kept pecking the ones i put in there with him and when i clipped his beak he still tried to but could not hurt them, and he stopped and it grows back very fast.
william