As the intro movie is playing, you need to input a specific button sequence. Press the X and B button, as well as the Up button on the d-pad, all at once. Once you do this, the game will ask if you wish to delete your save file, because it's super permanent. Select Yes, and it'll be wiped.
Also, how do you save your game in Pokemon Pearl?
How to Save Your Progess in Pokemon Diamond, Pearl, and Platinum
- Go to the menu by pressing the X button.
- Scroll down to the "Save" option and press A.
- Press "Yes" on every question the system asks you, and don't turn the power off until it is done saving.
How do you delete a game on Pokemon Pearl?
To delete your saved game, go to the Title Screen, then simultaneously press Up on the Control Pad, SELECT, and the B Button. Once your saved data is deleted, it CANNOT be restored. Please be careful when deleting your saved data. (All Pokémon and Items will be deleted.)