Just click download and tap OK to start downloading – then you should be able to see it downloading on the top bar of your device. Once it's downloaded, open Downloads, tap on the APK file, and tap Yes when prompted. The app will begin installing on your device

Allowing app installs from Unknown Sources in Android

1. Navigate to Setting > Security.

2. Check the option “Unknown sources“.

3. Tap OK on the prompt message.

4. Select “Trust“.