This needs to be done in each course.
Select Grades to go to your gradebook. Then select the gear at the top right.
Check the box next to Automatically apply grade for missing submissions. Note: this step is options. Please remember that if an assignment does not have a grade entered it is not counted in the grade and is effectively excused. If you don't complete this step, you would need to enter zeros for all grades that are not submitted.
Select the Grade Posting Policy tab. Select Manually Post Grades. Then select Update. Note: this policy allows the grade to be hidden from the student and parent grade view until you post the grade. This keeps them from seeing the grade until you have completed grading it.