To edit a submission you have already made, click on the edit (pencil) icon on your dashboard. You can edit any submission, even if it is complete, subject to deadlines and settings.
You can also amend by clicking on the name of the file...
Make the changes required to your submission then click on Submit.
If submissions are closed, the grey pencil icon will be greyed out, and clicking on the title link will direct you to a read only version of your submission.
See also Making a submission.
If you can’t find the guidance you need, please contact: email@example.com