If you provide more context (emulator vs. real Switch, whether you have your own keys), I can give more specific guidance within legal bounds.
NSP (digital eShop format) is a common process used by Nintendo Switch homebrew users to improve file compatibility and storage efficiency. Core Informative Features of Conversion Storage Optimization: XCI files are raw cartridge dumps and often contain "padding" (empty space) to match physical cartridge sizes (e.g., 4GB, 8GB, 16GB). Converting to NSP strips this padding, resulting in xci to nsp