You can copy a complete plan by clicking on the copy-icon in the “Plans” tab. If you want to copy a design from one floor to another, you can click on the copy-icon in the menu that shows your designs (in the 2D application). Hope this helps.
If you want to copy a complete project you can click on the icon with the two white papers. It’s located on the right side of each project name, just before the delete icon (the red cross).