i don't have the config file

Hello, depending on what Minecraft version you use, finding server config files can be a bit tricky. Try searching both the config folder (at the same location where the mods folder is) and the serverconfig folder inside the world folder (and that world folder is again at the same location than the mods folder).
I'd appreciate if you tell me whether you've now found the config file, so I can close this issue.

found! It was at the server config inside the world wolder thanks you!