If you are having trouble accessing the update on the eShop, ensure your Nintendo Account region matches the game's region, as some content is geo-restricted .
: Users with custom firmware often use tools like Tinfoil to manually install NSP update files from their SD card. Key Improvements in Recent Updates Elderand Switch NSP Update (eShop)
How to Install NSP Files from SD card to the Nintendo Switch using Tinfoil!!! If you are having trouble accessing the update