If you cannot remember your 4-digit PIN or want to reset it, select "Forgot your PIN?" at the bottom of the blue "Enter your PIN" page. You will be logged out of your account and once you sign back in you will be asked to create a new pin.
If you do not see "Forgot your PIN?" at the bottom of the blue "Enter your PIN" page, you are being asked to create a 4-digit PIN because the "Forgot your PIN?" option is only shown once a PIN as been set for the account.