Resubmit an Assignment
From EdTech Help
If an instructor has permitted resubmissions to an assignment, students will be able to resubmit via the assignment's textbox or as a freshly uploaded document.

Ensure that you remove the contents of your previous submission before resubmitting! The steps to doing so are described on this page.
Contents
Resubmit an attached document
Visit the Assignments tool
Select the Assignments tool from the Tools Menu in your site.
Click on the title of the assignment
Remove your previously submitted document
Use the Remove option to delete your previously submitted document.
Attach your new document
Click Choose File to select a new document from your computer.
After uploading your new document, it will display in the Attachments area.