Hi @johnathon0!
I had a quick look at the plugin, in the plugin settings you are able to set this as a setting, letting people be able to choose between classic and block editor. But since you are asking about only removing this possibility for authors, I am guessing you are aware of this setting and want to keep it for administrators.
Seems there isn’t a good filter or a snippet to do this, it is possible through user capabilities filter, but I wouldn’t recommend it. The reason is if some admin is changing a post from block editor -> classic editor, the markup isn’t the same, meaning it could lead to unexpected and likely breaking posts.
So I would recommend either disabling the option for everybody, or leave it on so everybody can choose.
