Follow these instructions to link a Nintendo Account.
❶ From Menu on the title screen or the Misc. menu within the game, select Account Management.
❷ Select Create/Link a Nintendo Account.
For customers that have linked a Nintendo Account:
If you previously linked Fire Emblem Heroes to a Nintendo Account and wish to link that Nintendo Account again, you will need to delete and reinstall the application and link your Nintendo Account during the initial setup.
If you link Fire Emblem Heroes to a Nintendo Account, you can later recover any app data that has been backed up to that Nintendo Account.
Please note that if you delete the save data linked to your Nintendo Account, you will not be able to recover it later.