Format: 

Author, A. A. (Year). Title of case study. Retrieved from URL

Author, A. A. (Year). Title of case study. Location: Publisher.

Examples: 

Suitt, H. (2003). A blogger in their midst (HBR case study). Boston: Harvard Business Publishing.

In-text: (Suitt, 2003, p. 3)

Suitt, H. (2003). A blogger in their midst (HBR case study). Retrieved from https://cb.hbsp.harvard.edu

In-text: (Suitt, 2003)

Suitt, H. (2003, September). A blogger in their midst. Harvard Business Review, 81(9), 30-40. Retrieved from http://www.hbr.org

In-text: (Suitt, 2003, p. 33)

Notes: 

If the case study is published as a standalone document, cite it as you would a book. Otherwise, cite the case study as an article.

Source:
APA - 7.02, no. 18-19