How can I edit previous days?

Editing previous days is quite easy:

The first step is to tap on Logs. Locate the left arrow near the top and then tap on it to return to a former day or tap on the calendar to locate the date. Now, you can add foods like you normally would by tapping on foods on the Grid. When you are finished logging foods to your day, tap on the right arrow until you have returned to the current day.