To "put together" or merge a multi-part file like CONTRA-ROGUE-CORPS-nsp.rar (which usually implies it is part of a split archive like .part1.rar , .part2.rar , etc.), you need to use a file extraction utility to combine them into a single playable .nsp file for the Nintendo Switch.
How do I combine multiple part roms together : r/PiratedGames CONTRA-ROGUE-CORPS-nsp.rar
: Ensure every numbered part of the archive (e.g., part1.rar , part2.rar , etc.) is in the same folder. Use an extraction tool : To "put together" or merge a multi-part file