Write the rightsholder, which stands for either an individual or corporate author of the software, followed by year, title of the software, version number, description of form and from where you have got it.

Basic format:

Rightsholder. (year). Title of app (Version number) [Mobile application software]. Retrieved from https://xxx

References:

Skyscape. (2013). Skyscape Medical Resources (Version 1.17.42) [Mobile application software]. Retrieved from https://itunes.apple.com

Note: Android apps should have similar address: https://play.google.com/store/apps

In-text citation:

• (Skyscape, 2013)

Read more about this on APA Style website: Mobile App Reference Work