What is the most logical next event?

How to remove a henna stain
Mix equal parts salt and olive oil in a bowl.
The oil is an emulsifier, while the salt is an exfoliant, so the combination works well to get the henna off of your skin. You can use any kind of salt you wish.
You could use baby oil if you don't have olive oil. Soak a cotton ball in the mixture and rub the stain with it.