It’s not September 1st yet, so you can’t download the games via the Ambassador Program. But Nintendo has shared instructions on how to go about it once they’re online. The instructions are after the break.
1. From the Nintendo 3DS HOME menu, select the Nintendo eShop icon.
2. Scroll left and select “Settings / Other.”
3. Scroll down and select “Account Activity” to view a list of transactions.
4. The NES game will be listed here once it is available to download. Tap “Software Info,” and then “Redownload” to begin the download process.
Now continue to play the waiting game.