You can download the grades report for a selected assignment. For this, click on the assignment from the Graded category.
The Grading Breakdown page loads. Click on Download Grades.
A .zip folder with a CSV file inside it will download to your computer.
When you want to download grades for all graded assignments for all of your class sections, navigate to the Assignments tab and click on Download All Grades.
A .zip folder containing CSV files will download to your computer.