In the event that you do not select “Allow automatic export to grades” before students submit their quizzes, then you can check the box at any time in order to send grades to the gradebook automatically as long as a grade item is created for that quiz.
The pictures below show what happens if there is a grade item but “Allow automatic export to grades” is not checked.
As you can see, student’s attempts appear, but their grades do not.
To make learner’s grades appear in the case of quizzes with only multiple-choice questions, you can tick the box at any time and the grades will appear in the gradebook.
If the quiz has a written response component as well as multiple choice questions, then you must mark the written component before the grades are exported to the grade book.
As always, be sure to create a grade item before checking the automatic export box. If you do not initially create a grade item you can still create one later, check the automatic export box, and have grades go to the gradebook automatically (even if students have already submitted).