First “rename” your notebook using “File → Rename” to get it out of the way (and save it). Then click “Help → Lab Help → Get Latest Version”. That will give you a fresh unmodified copy with the “standard” name (the one opened by clicking “Work in Browser”). Now you can rename things back and/or “copy/paste” in whichever direction makes the most sense. The one other important thing to realize is that the grader only grades the notebook opened by “Work in Browser”, regardless of where you click the “Submit Assignment” button. Meaning that you need to be conscious of where you are doing the “real work”. If it’s in a notebook with a different name, you need to plan for a “rename” before you want it graded.