Hi Louise
The only way I can think to find one student's attempts over multiple SCORM activities and/or courses would be a database query to find the activities then manually remove his/her result.
You could also test removing the student from a course then adding them again - in previous Moodle versions the user's grades would appear back into the course but in 2.x their grades are moved to the history table so do not appear as current grades. I think there are a few who disagree with this and want the old behaviour back so be careful as this solution may not be permanent...
Good luck
Teresa