You can...but it isn't pretty. Or very safe. One wrong click...
If you have Adminer...and you have the student id and course id and maybe activity ID. And you delete quiz, scorm, lesson, etc attempts. You can go to the mdl_course_modules_completion and the mdl_course_completions and delete those completion entries within the database. It is pretty detailed and complicated...and dangerous. You can easily delete the wrong thing and mess stuff up.
It can be done. Doesn't mean it should be done. If you're just putting up a new version for re-completion, I'd make a copy, add the updates and enroll them in the new version--this keeps your data intact, if that's a concern. I'm kind of fanatical about keeping records (we have a retention policy that requires at least 5 years records retention, so deleting data is generally a poor choice for us).