There's a picture here that you may or may not find helpful. I've heard people describe the capsules containing the fine seeds as tiny footballs, seems appropriate. You can just locate the pods (capsules) and crumble those to sow.

Here is a link that might be useful: Butterfly seeds

The flower bracken will produce hundreds of little football shaped pods standing on end. It takes a couple months for the pods to develop and ripen after the flower fades. When the pods turn brown (usually well after the freeze in zone 5) the seeds will be ripe. If you let them stay on the plant long enough, the pods will crack open. Carefully clip the whole bracken into a bag and give it a shake and you will have a million little yellowish "hairs" fall out. Those are the seeds!

If you don't let the pods crack open after they are brown, just gently crush the pods and sow chaff and seeds. Unless the pods crack open, it is impossible to separate chaff from seed but that is no big deal.