Hello,
If it is for a server you can use the plugin Multiverse-core to import a map to drag the map (for the example I will call it "murder") to the same level as the world map after you have just a Do the following command / mv import murder (replace murder with the name you gave the map)!
There are other ways to do this.
In solo it is simple you take one of the maps you drag it into the file saves that is in your .minecraft then you launch your game and you go solo.
Thanks you for this review !
sorry for the delay but i go add these new map ^^