You might need to change your phone's settings to permit installations from unknown sources after downloading the APK file to your device. Making sure that your device can run rummy appapps from sources other than the official Google Play Store requires taking this step. Go to the settings menu on your device, choose "Security," and allow "Install Unknown Apps" for your file manager or browser tool to accomplish this. To start the installation process, find the downloaded APK file in the file manager on your device and tap on it.