Select the Nintendo eShop on the menu to launch the Nintendo eShop.

Select the account you want to use to the code for

Select 'Nintendo Switch Online'

Select the “Check/Change Membership” to see the plans

Scroll down to 'Redeem Code' and select 'Enter'

Enter the code you received from us

Select 'Confirm' to redeem the code

Please read https://www.nintendo.com/giftcards/terms/