Depends on what you're trying to achieve. If you want to start the page from scratch (or just clean up the list) - then as stated above you can't. But if you need to prepare a different version submission - all textfields seem to be editable when in "Prepare for Submission" state. So you can replace your build, rename the version etc, so basically overwrite the whole page.

Any updates / solutions on this?

Found the mistake on my side. I already had installed release version of the app (same bundle id). Deleting release one did the trick, now I can debug NSE as expected. pluginkit and this SO answer helped

Succeeded to restore the resizing functionality by opening new tab..