Since .7z is a compressed archive format, the playable game file is usually just sitting inside it. : Download and install the 7-Zip tool.
To understand why this tool cannot exist, you must first understand the two file types involved. 7z to 3ds converter repack
Select 7-Zip > Extract Here . This will unpack the contents, revealing the playable .3ds or .cia file. 7z to 3ds converter repack