First of all, please make sure you know and tell which nintendo account you are using.
1. Click on System Settings
2. Go to Users and click the primary account that you are using
3. Make sure is email is shared to the Family Group Admin in order to allow you join the group.
4. You will receive email once the Family Group Admin has added you and click on the link in that email in order to join.
5. Click “Join family group” to accept the request.
6. Now are part of the family member, Hooray~!
7. In order to check the status, please download the Nintendo Online App in you Switch to see if you can enjoy the Nintendo Entertainment System (NES) game.