One of the most reliable ways to convert 7z files to 3DS format is to use dedicated conversion software. Here are the steps:
Once you have the .3ds file, you must point your emulator (like Citra) to the folder where the extracted file is saved .
Leo frowned. He tried "Extract Here." A progress bar jumped to 100%, but the file didn't appear. It was a ghost in the machine. The archive was locked, or perhaps the header was damaged. He couldn't just open it; he had to convert it—extract the raw binary data from the compressed container and rebuild it into a usable cartridge image.