To transfer your progress from one device to the other, you need to ensure that Shadow Fight Arena is not already installed on the second device. If the game has never been installed on the second device, then:

1. Download and install Shadow Fight Arena.
2. Install Google Play Games (Android) or Game Center (iOS) and connect the account you need. Progress will be restored in the game on the second device.

If the game was once installed on the second device, then you need to do a factory reset on the second device and not log in to the old account, but log in to the account that you want to transfer. Then you need to connect your Google Play Games (Android) or Game Center (iOS) account.