@duck19 What was helpful for me to know is that you can't overdose them. It won't hurt them if they get a little too much as their bodies won't absorb it.
That one works! I did put in their water but that was just an extra avenue - I know they spill. I was fermenting food so added it to that. Others put it over treats. You could also carefully syringe it in. I think @Miss Lydia was advising on how to do that with a duckling.
Yes, Pekins are bred to be meat birds harvested at 8 weeks old, so they put on weight more quickly than their bodies can handle sometimes. They need more niacin than is provided in brewer's yeast or the regular food. Your pekin needs liquid vitamin B complex ASAP. You can get it at tractor...