If a submission has been delivered to ProQuest and is not yet published, ProQuest is able to "undeliver" the submission so that edits can be made. Please communicate with your academic department coordinator to start this process. ProQuest will change the status from "delivered" to "ready for delivery" at which point you will be able to upload a revised PDF copy before re-delivering. You can do that in the Revisions/Changes section, where you will be able to Replace the existing PDF with the revised PDF.
