I just spent a good half hour trying to find a method to erase the save data (trophies, records) on the Nintendo 3DS.
It turns out the method for the original DS DOES work!
Why am I posting a topic about it, then? Because even after I knew it worked, it took me 10-15 minutes to press these buttons and get it to the delete screen. I almost gave up.
Hold down select first, then hold down L (if select isn't held, the camera will activate), then use a third finger to hold down the right directional button. Here's the hard part: Pressing the game icon while holding down the right directional, since it causes it to scroll to the right.
Just keep mashing the touch screen icon to start the game and eventually you'll get it. Also, this will boot the game in original resolution so it will look smaller. Select "Yes" to delete data. It will take about 1-2 minutes.
Then you can play! Feel free to reset and restart if you want the default game size.
Again, just figured if anyone is going through the used DS cheap games on their 3DS this info might help them not give up on trying to delete the data as theres very little info about it.