In a large bowl, combine baking soda, citric acid, epsom salt and cornstarch. Add in dried herbs if using them*. Mix well to get any clumps out. Add in essential oil and coconut oil, and give it a good whirl. Slowly add in water, stirring after each addition. It'll fizz a little as you add in the water.

You can divvy this mixture out into ice cube trays, different molds, or use a meat baller to form balls. You could even free form them with your hands, although they might not look as nice.