The Virtual Seed Tray program (Enhanced Version) must be running (and Plant Tycoon must not be running). Click on Tools, then Chart. On the chart, click on a place on the grid that represents the plant you want to mutate to or from. For example, if you click on the very upper-left square, you'll see the information for a Spotted Reptans. Look at the screen shot in this post, and you'll see where it tells you what you could get if you want to use the Mutation Liquid (look in the area that's circled - in this case it's a Lilia Astera).