Here's the dosage for Equimax, post #1 in this link:
https://www.backyardchickens.com/threads/treating-tapeworms-under-construction.1220309/#post-19519143
Valbazen can be used; however it requires higher doses, multiple days of withholding feed and repeated dosings through my personal...
Those are tapeworm segments. You'll need to purchase Equimax equine paste at a feed store to treat them.
You'll need only to treat the infected chicken(s) that excreted/excrete the tapeworm segments.
Small white worms: A pic would help to determine if it's cecal worms or tapeworm segments or maggots.
For cecal worms, I recommend Valbazen or Safeguard liquid goat wormer.
For tapeworms, I recommend Equimax equine paste.
For maggots, check for fly strike.