From the console U HOME Menu, select the Nintendo eShop icon.
Select "Balance" or press the + button.
Select "Add Funds with a Nintendo Prepaid Card."
Enter the activation code from the back of the prepaid card, then select "OK" to complete the transaction.
When you enter the card's activation number on your Nintendo 3DS, Nintendo Switch or Wii U system, the card balance will be associated with your Nintendo 3DS, Nintendo Switch or Wii U System and will be non-transferable. There will be no remaining balance on the card.The card balance may only be used on a single Nintendo 3DS or Wii U system.