Do not do it.
: Sites focused on emulation, such as EmuCR or Romhacking.net, might host or link to BIOS files, often bundled with emulator releases or development kits. dsi bios files download link
To emulate Nintendo DSi games or use the DSi menu on emulators like melonDS or Delta, you need specific system files. While many sites host these, the most reliable and legal method is to dump them from your own console using homebrew tools. Required DSi BIOS Files Do not do it
If your DSi is already modded with Unlaunch, it is the easiest way to get the files. Use the tool by DS-Homebrew. such as EmuCR or Romhacking.net