"Take a bow"
Step 1: Lure Your Dogs Head Down to the Floor With a Treat
Make sure the butt is still up in the air; if they continue to go in a down use a leash to wrap around their back end to pull up as your lure their head down.
Step 2: When the Dog Is in Desired Position Click and Treat
When they are still in the bow position feed them the treat.
Step 3: Attach a Hand Motion and a Word to the Command
Like "take a bow" or "why hello" something simple-- and the hand motion should be something with your palm out motioning down towards the floor.