At the start of chapter 6 (the Heir hunt), you'll be tasked with completing a simple DNA minigame. Once you've completed it and made it back to Phil's dossier, close your DS. That's right, close the thing. (as if you're going to put it into standby mode) When you open it next, you'll be staring at the back cover of the dossier. Here, you can play either the DNA minigame or Tic-tac-toe, or go visit Madam Fate. (if you found her at the end of chapter 4) To go back, just tap the left-pointing arrow at the bottom left, which will bring you back to the dossier proper. You can go back to this area whenever you want (provided you're on either chapter 6 or 7) if you're not already investigating a suspect.