Hello. Is it possible to delete a mistakenly submitted assignment before it is graded

Hi! You can't delete an assignment that's been submitted. It's possible that you can overwrite it, but that will depend on whether you're allowed multiple attempts, and whether the assignment has been set up to keep every submission, or to only keep the most recent submission. Your best option is probably to reach out to the person leading the course and ask them to delete it for you.