If you need to award full-credit for a quiz or test question after students have already submitted, go to "Tools" > "Quizzes." In the quiz tool click on the caret next to the correct quiz/test and click "Grade"

Next, click on the "Questions" tab toward the top left of the page.

Next, click on the radio button next to "update all attempts" and then click the question you want to update.

Type the number of points in the box and then click on the blue "Save" button.

This will award all students that point value for the question regardless of their answer.