How to redeem:
* Using a browser, visit ec.nintendo.com/redeem/#/
* Select Sign in and enter your Nintendo Account e-mail address and password, and then select Sign in again. ...
* Enter your 16-digit download code and then select, Next.
* Re-enter your Nintendo Account password when prompted, then select Redeem to complete the process.

Notes:
You will receive the code instantly by email.
No refund on digital products.
No exchange for ordering the wrong region or type.
Exchange is allowed only if the code was invalid.