She pressed A.
boot9.bin cannot be downloaded legally. It must be dumped from a (like Luma3DS + boot9strap). The standard tool for dumping is GodMode9 .
Once you have installed boot9strap and Luma3DS, back up your SD card’s boot9strap folder (including boot9.bin ) to your PC. Along with a NAND backup, these files are the ultimate insurance policy against a bricked console.
It is the master key, the skeleton key, and the backup of the console’s most closely guarded secret: the security. Without it, modern 3DS modding as we know it would be impossible. With it, you can unbrick consoles, decrypt system files, and understand the inner workings of Nintendo’s handheld.