Need Start Course Over button if the student fails

It looks like course press shows completion of the project 100% as if you have been through the course - not whether you pass it or not. So we want to send people on the completion page to try again if they have failed. In the workbook, it says failed - but is listed as 100% as they have got to the end. So if it's failed we want to give them a retry button - because they've not really fully completed it successfully. Is there a shortcode to send them back to the start of the unit/course?