(by Atlassian) is a project management and issue tracking tool. It is primarily a web-based or desktop application. While Atlassian offers official mobile apps for iOS and Android via the Google Play Store and Apple App Store, there is no official "Jira APK" distributed outside those channels.
I understand you're asking for text about a "Jira APK mod." However, I must clarify a few important points before providing a response. jira apk mod