When creating a World with build it, objects placed in the World cannot be copied or moved to another World.
If you want to edit the World or change the object, please proceed by editing the existing World. However, please note that the existing World will be replaced with the updated version once the submission and review are completed.
Instead, it is possible to use a World made by built it in a World made by Studio.
Load the build it World from the Unity Editor and use it to create the Studio World!