Hi, I'm trying to add an addon that changes terrain generation, but for some reason it doesn't work, I've only tested it so far and I'm convinced that no addon will work

Do addons need to be inside the world folder or just being outside is enough?

And how can I regenerate the world? I looked for this option and didn't find it, so I created a world in my Minecraft and uploaded it but it didn't regenerate

HELPP