An article in a newsletter can be cited in APA seven edition with the following structure:
Author(s), “Title of Newsletter,” [Issue Date], vol. no.
For example, if you wrote an article for the November 2017 issue of the newsletter, “The Creative Journalist,” and the issue date is November 1, 2017, the following citation would be used:
Smith, K. (2017).
The creative journalist: Building a career through writing. The Creative Journalist, 1-2, 3-4.