You have to do this after installing from Google Play or APK and before launching the game on the new device or instance.

Save Locations:
[NA] Storage/Android/data/com.aniplex.fategrandorder.en/files/data
[JP] Storage/Android/data/com.aniplex.fategrandorder/files/data

You will have to copy these files and put it at the same location in your target device or emulator. They start with:

    54cc

    969b

    644b

    e1a9

Open up the game and it will show your friend ID on the bottom if you done it correctly.

Some notes:

    This will work for most Android devices and your favorite Android emulators.

    You can only play one device or instance at a time.

    No root needed.

    Any file explorer works. I personally use a paid app called Solid Explorer and it has a free 14 day trial if you plan to use it.