Assembly CS

Hello, greetings to everyone.
Does anyone have an updated tutorial on how to modify the assembly? I saw one here on the forum but it doesn't work, but I do exactly what it does and a lot of errors appear in DnsPY

Why ever modifying any assembly when you can have an always working Mod integrated directly into the game?
https://www.mpgh.net/forum/showthread.php?t=1576517