A Nintendo Switch Online membership is required to utilize the Save Data Backup feature.
Save data files can be manually backed up from the game's software menu or from System Settings.
Save data backups can also be set to run automatically.
Complete These Steps:
To back up save data from the software menu:
Open the game's software menu by highlighting the game on the Home Menu and pressing the “+” or “-“ Button on the Joy-Con.
Select "Save Data Cloud Backup."
Select the desired user, then select "Back Up Save Data."
To back up save data from within System Settings:
From the HOME Menu, select "System Settings" > "Data Management" > "Save Data Cloud Backup."
Select the desired user. Tap the software to back up, then select "Back Up Save Data.