I need to make an .asm program to save some values in a .txt file. Using C would be much easier, although I cant use it this time. Any idea how to do it?
Aseembler code will not magically save any data in any text file.
To have a text file, you must first have a file. To have a file, you must have a file system. To have a file system, you must have some form of drive. That drive is very hardware-specific - something you haven't mentioned anything about.
Take 100 steps back. Reconsider. Do something else.