How to update app store images on existing app

The documentation says I can update images when the app is in states:

Prepare for Submission Ready for Review

When I submit a new version it goes from Ready For Review to Waiting For Review within the same minute. Did I do something to make it go to Waiting For Review? Is it only in state Prepare For Submission before I submit the first version or can it be in that state for subsequent versions? Why do they make it so hard???

When and how can I update app store images on existing app?

Also, can app store images be updated from within the project using xcode. I had to add them manually for the initial setup.

How to update app store images on existing app
 
 
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