Until the Action App is in the App Store, it runs through TestFlight, Apple's app for trying new apps.
1. Install TestFlight from the App Store
Install TestFlight2. Come back here and join the Action App
Join the Action App3. In TestFlight, tap Install. The Action App appears on your home screen.
1. Open the downloaded file.
2. If your phone asks, allow your browser to install apps.
3. Tap Install, then open the Action App.
Your phone may warn that the app is not from Google Play. That is expected until the Action App is in the Play Store.