The best and easiest way to transfer your game progress from one Android device to another is to connect your game to Google Play.
To connect to Google Play:
Open the Google Play Store on your phone
Search for and install “Google Play Games” on your device
Open Google Play Games app and create an account or login if you already have one
Open Rivengard app
Tap on the Settings icon in top left corner
Tap on ‘Connect’ (green button)
The app will automatically try to connect to Google Play Games with your logged in account
When you play on the new device simply open the game, go to the settings menu and log into Google Play to retrieve all your progress.