The issue name is on the cover page and tells readers which edition of the newsletter this is.
You can use the automatic issue numbering ("Issue 1", "Issue 2", "Issue 3" and so on) or use your own.
In the Author (where you build the newsletter), next to the issue title on the cover page there is a pencil icon. Clicking this will bring up options for changing the issue title.
By default, each draft newsletter is assigned the next issue number when it is published. For example, if you have published 3 newsletters since the start of the year, and have used the auto issue numbering, then each of these newsletters will be named "Issue 1", "Issue 2" and "Issue 3". The next newsletter you publish will automatically become "issue 4".
If you want to use a custom name for a draft newsletter, or change the name of a published newsletter, click the pencil icon next to the name of the newsletter in the Author, and enter the custom name in the popup window that appears.
If you have published a newsletter, and it displays the wrong issue number or an otherwise incorrect title, click the pencil icon next to the name of the newsletter in the Author, and clear any text that is currently in the custom name text box, and update the issue number text box to the correct value.
If a draft is displaying the wrong issue number, click the pencil icon next to the name of the newsletter in the Author and update the issue number text box to what the next published issue number would be.