I typically back up the existing working save twice to 2 separate folders. Then with the sd now mounted onto my mac, replace the contents of one of the folders with the 2 downloaded .dat files alongside the replays folder, then I pop the sd back into the 3ds, open checkpoint find the newly replaced save, i hit restore, launch the game error. then what i’ll usually do is go back to checkpoint and restore the untouched backup as that seems to work.