You should see a link to "edit content" next to the video in your curriculum. Just hit that and you can upload a new video to replace it with. If you do that before a reviewer gets to it, then it'll be like it never happened. And even if they have gotten to it, they're only concerned with whether you are violating any policies, and don't really care if you uploaded the wrong video (unless the one you uploaded does violate a policy - if that happens, you should be allowed to resubmit it). You're still allowed to change and update videos after your course has been approved.