Navigate to the folder created by your save manager. For JKSV, this is typically located at SD:/JKSV/Super Smash Bros. Ultimate/ .
However, a major challenge is finding a save that matches your specific needs. Save files may work on a specific game version but fail on another. A common complaint on these forums is exactly this: users will often find a save file for the wrong version, like someone sharing a file for version when the game is far more recent, leading to frustration and wasted effort. super smash bros ultimate 100 save file
Unlike the PS4 or PC (where you can drag/drop a .sav file), the Switch uses an encrypted save system. You cannot simply put an SD card into your computer and paste a file. Navigate to the folder created by your save manager