You might have figured it out by now, but in case you haven't, I just discovered (by finding myself in the same scenario) how to edit the submission.

You go to the project from your profile, and in the top right there should be a pop-up-like box mentioning that said project is submitted for the game jam. Click on it. It will take you to a page where you should see somewhere on the right (above your submission details) a button for editing the submission.

In any case, this would be for updating the submission details, like assets used and source, but if you edit the project from your profile directly, it should update independently of the game jam submission. At least, that's the logic I found. I haven't tested it.

Hope this helps :)