The best way to create a two-day plan is to start by splitting the park. It's easiest to split it geographically -- say Tomorrowland, Toontown, Fantasyland one day and New Orleans Square, Adventureland, Frontierland, Critter Country the other. It can take some trial and error to get the plans to work out time-wise, but we do have a starting spot. We have two different two-day Disneyland plans for the Whole Family here: https://touringplans.com/disneyland/touring-plans/whole-family that can help. You can also copy the plans using the Copy Plan button at the top, which will save them to your personalized plans and allow you to modify them.