Since the official Google Play Store often fails to load on Android 4.1.2, you will need to manually install APK files from trusted archives.
Since the Google Play Store is largely inaccessible or non-functional on older devices (due to version mismatches), the most reliable method for an is sideloading via APK archives. android 4.1 2 jelly bean apps free download
Before downloading anything from the web: Since the official Google Play Store often fails