Make sure it's nutritional yeast and not baking yeast. Big difference. But when one is already has a problem liquid B complex is better.
https://www.backyardchickens.com/th...dicated-feed-the-myths-and-the-truth.1247838/
Info on liquid B complex and dose for age of ducklings.
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
I hope you helped the little duckling right itself when it was on its back. That can be very stressful for one.
It takes a little effort but you can get the top off the bottle without having to use a syringe to get the liquid out. Then just use the rubber stopper to keep it fresh and place in the frig. Don't give it cold to your young duckling though.
You may want to have 2 brooders going anyway the ducklings are much messier than the chicks and you don't want the chicks wet.
ideas
https://www.backyardchickens.com/articles/how-to-set-up-a-duckling-brooder.75719/
something else put the chick grit in a separate container from their feed they will use it as needed.