Menu -> Options allow you to link to the platform (Google,  iOS, Facebook) login. 

iOS: Game Center Link

Game data associated with your  Game Center account is automatically saved, you can use the same game data if you use the same  Game Center account on other iOS devices.

Game Center Account linking Steps:

1. Settings > Choose [Game Center]
2. Login with your Apple ID.
(Please create an Apple ID if you do not have one.)
3. Log in back to the game.
4. Game Center login message will be exposed on the upper side of the main screen while loading

Android: Google Play Link

Game data associated with your Google Play account is automatically saved.
You can use the same game data if you use the same Google Play account on other AOS devices.

Please review the following to sign in with your Google Play account.

※ You must have the Google Play Game app installed.
※ Please update your Google Play Game app to the latest version.
※ Google Play accounts only save one game data at a time!