oke first you need ida pro. not the free version. doesn't work with extensions. If you don't know were to find ida pro than you could always use ghidra. It's free and works almost the same.
For ida pro you need a switch plugin. Use this one:
https://github.com/pgarba/SwitchIDAProLoader.
To unpack a nsp. Follow this link:
https://gbatemp.net/threads/extract-nsp-nca-xci-update-all-in-one-tool-for-layeredfs.511156/.
When you have unpacked your nsp you get a main file. Open this in ida. Then you have to wait for the program to dissemble it. It can take a couple of minutes to a couple of hours depending on your pc.
If you're lucky and your nsp has assembly symbols you could look around and try to change anything.
When you found a address that you want to change copy the code for example: .text:0000007100444788
MOV X23, X4 to
http://armconverter.com/ and press convert. then you see ARM64 GDB/LLDB: AA0403F7. This is your code for sx os or atmosphere. So the code would be 04000000 00444788 AA0403F7.
There are more ways to do this. Like unity games use il2cpp. Than you can use this:
https://github.com/Perfare/Il2CppDumper/releases.