If you have been invited to present more information to the Project Owner in a Re-opened Project, you'll first need to log into the Portal and click on the My Opportunities button.
From there, click View Opportunity:
From the Project Details page, click Modify Submission:
From there, you will be able to upload new documents to any unlocked slots:
Once you have completed uploading your additional content, be sure to click Submit and Finalize to complete your submission.