that's because it has to be done through a special, unique link given to the quest creator.
Use this to resubmit, and you should be good to go.
https://itch.io/jam/326454/add-game/1918900/1381177?token=v2HVcgZJsqdIOlUyyZGv8AQR1g
Hey Ash,
Either I'm too stupid, or the system likes my original submission. Do I need to delete/remove the old one, as when I click on the link that you provided, it takes me to a screen to add my back into the Jam; it asks for my Handle, and the quest name, but nothing else. When I navigate to the screen to upload the new version, I see the attached message. Any tips or suggestions would be greatly appreciated. I'd love to enter this contest, but you are probably getting as frustrated as I am.
You'll have to nuke the old one. I think what others are doing is changing the submission itself in its own page (you can update or change files at any time when you upload a project to itch). Then using the link.
I removed the other one once more so you should be able to edit now, and then use the new following link to resubmit.
Don't try it until you've edited /uploaded your quest first, though!
https://itch.io/jam/326454/add-game/1918900/1381177?token=v2HVcgZJsqdIOlUyyZGv8A...
We'll get you in here. :) and sorry for this being frustrating. I knew it was going to be new for nearly everyone and hoped I would be able to work out the bugs, but didn't happen for some.