If you're dealing with gapeworms, here's a link. Covey Rise Plantation has dealt with gapeworms many times. Here's a link, post #'s 13 and 14 on how to treat.
https://www.backyardchickens.com/forum/viewtopic.php?pid=7931055
https://www.backyardchickens.com/forum/viewtopic.php?pid=7931055