158: How do I fix and resubmit a rejected Gnus posting?

  The standard buffer name for editing Gnus posts is *post-news*.  Assuming
  that you haven't used that buffer since trying to post the rejected
  article, you should be able to switch to it using C-x b or

    M-x select-buffer RET *post-news* RET

  Once in that buffer, fix whatever problems the message might have, and
  submit it again using C-c C-c.