Quiz regrade is available only for Multiple Choice, True/False, and Multiple Answers question types. Also, it applies only to students who have already taken the quiz.
Note that Quiz regrade does not apply to questions linked to a question bank since questions may be used in more than one quiz. Also, adding or deleting answers from a question with submissions disables the option to regrade that question.
For regrade options to appear, you have to:
**Regrade options will not apply until you have re-saved the quiz.
Check Canvas Documentation for more details:
Hope this helps!