Link in Re-submission email generated by ETD Admin.
In addition to the link, add the text "or log into your ETD Account to re-submit your revised manuscript. Students will often try to use the link after it has expired and email asking for a new link.
J. Christian Sweatt commented
I'm wondering why the resubmission link even expires if the submission is still active (hasn't yet been approved)?
As an alternate solution: why can't these links remain active until the submission has been accepted by the ETD admin? This would solve the issue altogether.