To access the password screen, you need to press Up, Down, B, Down, Down, B + Up, B at the title screen.

Password guide: https://imgur.com/a/qudqBzi

There are more passwords in the game, but those are the cards I use.

Ultimate spreadsheet: https://docs.google.com/spreadsheets/d/1indyZdZP51m7NyARRI0kGKDIYAX8vaeI11SLRO7-goE/edit#gid=2001656742

Information is sorted by the tabs on the bottom of the google doc.

To delete your save file, you need to press Down, Up, B, Down, Down, Right, Up (x4), B + Down at the title screen.