Create a folder named NSPs on the root of your SD card.
If you don't want to remove your SD card, you can use a USB cable and NS-USBloader. Pic-a-Pix Deluxe Switch NSP Free Download
Open Awoo Installer or Tinfoil on your Switch and select Install over USB . Create a folder named NSPs on the root of your SD card
You can purchase and download it directly from the Nintendo eShop . Pic-a-Pix Deluxe Switch NSP Free Download
To use NSP files, your Nintendo Switch must be running like Atmosphere. A Modded Switch: Must have a working homebrew environment. SD Card: Formatted to FAT32 (recommended for stability).