This is a very simple love charm, though you might have to search a bit to find a sprig of yarrow. It has to be a whole section with stem and flower cluster, not just a handful of chopped pieces.
All you need to do is hang the sprig of yarrow over your bed on a piece of string, so the flowers are pointed downwards. The catch is that it should hang over the middle of your bed, so you can’t just dangle it from the bedpost. You can put a small hook in the ceiling and hang it from there, for example.
It will bring love into your life, but you should take it down immediately after you meet someone.