There is a long standing idea conversation still open about this that you might like to join: https://community.canvaslms.com/t5/Idea-Conversations/Delete-quiz-attempts/idi-p/37627
In new quizzes we now have some additional moderation options that should limit the need to exclude an attempt:
In the instructor view of the quiz there is a moderate tab. On the moderate tab, there is a list of attempts. You can manually submit attempts that get stuck as "in progress." You will also see a moderate button at the far right of the page. Clicking that button gives yo the ability to reopen (and add time to) those attempts that students have an excuse for. Rather than delete or exclude, this offers a way to fix a disrupted attempt.
In my own courses, I don't use the average as a way to calculate the score for multiple attempts in my own courses, and so I generally only need the option to allow another attempt. The options are all there together.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.