Hello! i don't know how to change the weapon parameters in the mrcrayfish gun mod to damage, rate of fire, and something like that. Who knows how to do it?

Heya, you need to create a data pack for that. This is as simple as copying the "data" folder from the mod (open it up as a zip file) and putting that within a "datapacks" folder within the .minecraft directory (make one if there isnt one). Then you just need to create a new folder inside the datapacks folder, call it anything, then copy over the pack.mcmeta and put the data folder from before and you're good to go! The gun data is stored under data/cgm/guns