If you need to edit a question in Canvas, you have to edit both the question as it is in a quiz and in its Question Bank. If the question is used in multiple quizzes, you will have to fix it in each quiz.
Editing a Quiz Question in a Quiz
Go to your Canvas course, then select Quizzes in the course navigation.
Click the name of the Quiz where the question is stored.
Click the Edit button. The quiz Details tab opens.
Click the Questions tab to view the Quiz questions.
Mouse over the question you wish to edit. New icons will appear below the question title in the upper right.
Click the Edit this Question icon. The Rich Content Editor (RCE) opens.