The documentation below demonstrates the process involved in updating scores on a quiz. This can be used when you have either incorrectly marked an answer or want to give credit to an answer that previously received none.
*Note: The screenshots/steps below show this process when regrading a true or false question; however, other quiz question types follow the same type of process.
Log into your course and from the Assessments drop-down menu click Quizzes.
To regrade all attempts select Update All Attempts. Then select the question you want to rescore.
Scroll down to the Grade heading and re-score accordingly by selecting either Give to all attempts __ points or Give to attempts with answer. Click Save.