If a student inadvertently submits the wrong version of a piece of work to a Turnitin Assignment they will not be able resubmit their work until you remove the original submission. This can be done quickly by any instructor. The short video below show s the steps to do this.
CONTROL PANEL> TURNITIN ASSIGNMENT> VIEW >find the student submission, select the check box next to their name and click DELETE. The student can now resubmit their work. Remember that this will show as a 100% to the first submission. This can be removed to see any underlying matches by viewing the originality report and deselecting the first submission as a source (it is not permanently removed).
Instructions can also be viewed on Turnitin’s help centre: http://www.turnitin.com/static/knowledge_base/deleting_submissions_from_inbox_newtii.html