Downgrade apps already installed just need the old APK file!
(*ROOT NEEDED*)
-Have the apk you want to downgrade at HAND!
-Make sure you the app you want to downgrade installed already.
-Click select APK (The older version of the app)
-Then click install
I was give permission to upload this app on the Google Play Store.
Credits: Pyler (He made the APP! Thank him on XDA).