From the Zinio Pro Publishing Platform Dashboard, click on Content > Issues to access to Issue Management Page
Under Issue Management Page:
1. Make sure the Tablet or Mobile tab is selected
2. Hover mouse over the issue you want to change/add cover image
There are two ways to change/add image:
1) Drag and drop your image file into the issue
2) Click on the text and a new "Browse" window will appear. Select the image you want to add to the issue.