If you've forgotten your password and can't log in, you can reset it via the "Forgot Your Password?" link on the login screen. There are detailed instructions below.
Be careful not to confuse your password with another.
If you've forgotten a child account password, see here.
If you've forgotten your Parental Controls (for parents/guardians to limit play) PIN, see here.
Password reset procedure (if you can't login)
1. Open the Nintendo Account login screen, and select "Forgot Your Password?".
2. Enter the email address registered to your Nintendo Account and select "Submit".
3. You should receive an email. Follow the link to the password reset page provided.
If you receive an "Access Denied" error when you follow the link, repeat the procedure again from step 1.
4. Enter the required information to confirm your identity.
Use the nickname or date of birth you entered when registering your Nintendo Account.
5. Enter your new password.
When the following screen appears, the password change is complete.
If you don't see "a new password has been set" displayed, it means the password wasn't changed. Please log out on this screen, then repeat the above procedure again from step 1.