You need to hack and CFW your 3DS (you can search for it on the internet how to do it), and after that you need to install TWPatch.cia into your 3DS, it'll show up in the Home Menu.
After that you can just use the + Control Pad to move the cursor up and down, but instead of A you hold START.
Before the patch will work, you'll have to turn off your 3DS, wait until the blue Power LED turns off, then press and keep pressing SELECT, press Power button, and hold SELECT until the screen turns on. If you did the 3DS hacking and CFW right, you should have an option to "Enable external FIRM loading". Go there, press A to make it an X, and press START to save.
Now when you launch a DS game, it should have the filter you selected!