When you’re ready to play with a second player, you can press the second Joy-Con down toward the Nintendo Switch system to power it on. Press L on the second Joy-Con to create a new princess.
Choose a princess on the left side of the screen with the Joy-Con, then scroll through the princesses you want to choose one, and finally press the A button to lock in your choice. On the right side of the screen, the same process can be repeated to choose the second player’s princess.
Once both players have chosen a princess, press SL or SR on either controller to choose a level to play. You’ll then be taken to the level select screen, where you can use the Joy-Con arrows or the L and R buttons to navigate. If you want to exit out of the level select screen, press SL or SR again.