Using eShop requires updating the system to the latest version, or using eShop requires a Nintendo account.

Select "(User Information) ァカント _" → "(Increase Balance) Remaining Height の" to recharge; The first item is a credit card, and the second item is a recharge card. Recommend prepaid cards for easy purchase. After selecting the recharge card, enter the card code.

The above is the switch recharge tutorial, I hope it will help you.