Hi, Priya.
Welcome to the community! You posted your question under the general AI Questions category, but you’ll be more likely to get the attention of the right people if you post it under the Course Q & A topic for your course. I changed the category for you by using the little “edit pencil” on the title. I’m not a mentor for that course, so am not familiar with the assignments there. But the first question is where is dataset defined earlier in that notebook? Maybe you have not run the cell that defines that yet. Just having the cell sitting there does nothing until you actually run it. Or maybe that cell threw an error when you ran it. Try “Cell → Run All Above” and see if that helps. Use the ^F search in the browser window to find the string “dataset”.
If that’s not the answer, then we’ll have to wait for someone more familiar with the course to help out.
Regards,
Paul