I know where the config file is, I just want to know how to change it from NORMAL to UNISON without having to do it in each new world. If instructions could be as clear as possible, it would be great because I'm a noob at editing config files and just coding in general.

There's a defaultconfigs folder in the main Minecraft folder where you can put a copy of the config you have in serverconfigs and it'll load that file as a default for each new world. Just put your desired colytra-server.toml in that defaultconfigs folder and you're good to go.

thank you very much