There are a few ways to run this but the easiest way in my view to do this is to download the files form GitHub and place the sl_dec.exe (in the bin folder) into the folder that has the .sl files you want to convert to txt. Then run cmd and path to the file that has the .sl files and the sl_dec application. Run the command:
sl_dec nameofdesiredslfile.sl
to extract the sl file you want to convert to .txt.
***Before doing the next step, back up the .sl file you are changing in a different place***
Change what you need on the txt and then run
sl_dec nameofmodifiedtxtfile.txt
to convert back to a .sl file.
There are some other commands like bulk converting .sl files to .txt and vice versa. Comment below if you need to know that as well =W=. Idk if you know a lot about CMD so I added some images that may help.