To duplicate an assessment, click the 'Duplicate' button under the old assessment heading, enter the new assessment name and select the course.
Duplicating an assessment will copy the answer key to the new assessment, but will not transfer any of the results.
GIF: Duplicate > Enter Name > Select Course > Duplicate
To duplicate a course that is listed as a 'Past Assessment', Select the 'Results' menu dropdown arrow and select 'Duplicate Assessment'.
You can then enter the new assessment name and select the new course.
Image: Results Dropdown menu, Duplicate Assessment.