The 7th edition of APA does not differentiate between the format of the books, print or electronic. Cite both the same way. If you have an open-access eBook, you may provide the URL at the end, provided it directly takes you to the full text without logging in.
Author, A. A. (Year). Title of book. Publisher. https://doi.org/XXXXXX
George, M. W. (2008). The elements of library research: What every student needs to know. Princeton University Press.
Kleiser, G. (2008). Fifteen thousand useful phrases. Funk & Wagnalls; Project Gutenberg. http://www.gutenberg.org/etext/18362 (Original work published 1917)
Samanez-Larkin, G. R. (Ed.). (2019). The aging brain: Functional adaptation across adulthood. American Psychological Association. https://doi.org/10.1037/0000143-000
Note: When citing in-text, it can be difficult if your eBook does not have a page number (most PDF books do). In this case, try to get as specific as possible by mentioning chapter, section, and paragraph numbers.
One of the author's main points is that "people don't rise from nothing" (Gladwell, 2008, Chapter 1, Section 2, para. 5).
Source: Publication Manual, 10.2 (examples 20-26); Book References [APA Style]