No need to knock out as it is a passive tame. Berries is best if a player does not have Rare Flowers. Easy tame, however, annoying because it will continue to walk around. Trapping it in a small area would best make it an easier tame and less wandering.
Once tamed, petting the Lystro will give experience boost to any dinos as well as players that are in its radius. I believe it lasts 5 minutes. So, when crafting a bunch of items, pet these little dogs.