- Visit https://www.nintendo.com/. Login to an existing account or create a new one.
- Click on your username and select ‘Settings’.
- On Settings page, select "Shop menu" from the left side menu.
- Select “Add Funds” and on next page, click “Prepaid Code”
- Enter the code you received from CDKeys and click redeem.
Or You can simply visit https://ec.nintendo.com/redeem#/ and enter the code and login to your Nintendo Account to redeem.