Adding worlds to a group

To add worlds to a group, you need to use the command /world group add <world> <group>.
The <world> argument is the key of the world you want to add, and <group> is the name of the group you want to add it to.

Example

Adding all farmworlds to the group "farmworld":

/world group add farmworld:normal farmworld
/world group add farmworld:nether farmworld
/world group add farmworld:the_end farmworld