You might do better to tell us what you tried, and how it failed.
I say this because it isn’t something for anovice without resources to take on.
By resources I mean something like a linux system with internet access and a working SD Card reader/writer.
You’re much better off finding out what’s wrong with your system.
The installer and disk images DO work just fine, if they don’t work for you, you have some hardware issue that needs resolving. There is no “manual installation” that is going to resolve a hardware problem.