If you have a 3DS console running Luma3DS custom firmware, GodMode9 is the safest and most efficient tool to convert and repack your files.
If you are planning to play the file on an emulator like Citra, a raw dump from a game cartridge might be encrypted. You will need a decryption utility: Download a trusted tool like . 7z to 3ds converter repack
There are two primary use cases for this workflow: If you have a 3DS console running Luma3DS
A compressed file container that uses high-ratio LZMA compression. Distribution sites use 7z to drastically reduce file sizes for faster downloading and reduced storage costs. The console cannot read a 7z file directly. 7z to 3ds converter repack