In Newsstand, your app will show the cover of the latest issue once you added it to the content media platform. To ensure, your latest issue will be visible in iTunes too, you should update the cover image in iTunes connect by following these few steps:

• Login to iTunes Connect

  

• Select your app

  

• Go to the Newsstand section (by pressing the Newsstand button)

  

• Add issue

  

• Enter all necessary information and upload the cover image of your latest issue

  

• Apple will need some hours to update the cover image in iTunes