Place your file into the nsp folder on your SD card. Open the Tinfoil app on your Switch. Navigate to File Browser > SDMC . Find your update file, select it, and choose Install . Using Goldleaf
If you are managing backups on a modded console using Custom Firmware (CFW) like Atmosphere, you will need to manually install the update file. super mario odyssey switch nsp update install
Tinfoil is a popular tool for installing NSP files directly from an SD card or via USB. Place your file into the nsp folder on your SD card