Hello! You can not actually duplicate a quiz within Canvas, you can only do this with assignments. However, there is a work around for copying quizzes. When you are in 'Quizzes' in the Course Navigation. You can click on the pancakes (three dots) to the right of the quiz you want to copy. Then click 'Copy to'. On the right you will get a side window that appears. You then want to select the same course you are currently working in for the copy to go to. Then click 'Copy'. You will then need to refresh your screen in order for your 'copied exam' to appear.
The copy will be its on entity and therefore you can make the necessary edits.
All the best!