btw you are trying in a 3DS or DSI ?
either way there is no way you can just put in the sd card and run it like that, the console will not care about it (stuff has security measures to prevent stuff like that)
the game even if it was free it's considered like any other paid game, it's nintendo propriety...
in the 3ds, if you have a 3ds with cfw (
https://3ds.hacks.guide/ ) install freeshop or similair, and you will be able to get it (or in sites that host roms, you might find a .cia for that game, you just have to install it trough the fbi homebrew or similair)
for the DSI, see the post user jdbye just said. i don't follow the DSI stuff, but its a different process