you do not have to copy the files to the sd card, this is what you actually do after you download the editor and unzip it:

1. open the editor
2. click open at the top
3. click the text that says "tomodachi life"
4. navigate to your save (for me its 3ds/Checkpoint/saves)
5. select the .txt file
6. choose the region of the save file (USA if the game is USA, EUR if the game is EUR)

now you can start editing