Carb cycling is when you vary the amount of carbs you intake on a day-to-day basis, usually to get more carbs on your workout days and fewer carbs on your rest days. The specific cycle is up to you, but as long as you can fit the whole cycle into a week, you can set it up with Eat This Much.
The main screen you'll want to look at is the Weekly Planner Layout page - you can find this in the "Settings" menu.
Lets take a look at this example weekly planner layout:
Each day can be set up with a custom set of nutrition targets. Here we just use two different nutrition profiles, "Rest day" and "Workout day", but you can set up a custom one for every day of the week if you choose.
In a very basic carb cycling program, I would probably set a high carb target on my workout days, and a low carb target on my rest days. Once you have the layout set up the way you want it, go back to the diet planner page and hit the button that says "Regenerate entire week...", and select the weeks you want to regenerate. Once you regenerate the week, the plans will be updated to match your new weekly layout.