The game can be connected to several identificators with the help of which in-game progress can be saved, transferred or recovered again. Those are Facebook, Google Play and Apple Game Center.
You should be logged in at least one of the above.
Facebook is the best option to recover your farm especially if the recovery of progress happens on devices with different operating systems.
Entering the game the window with “Yes, download this game” or “ No, save this game” popped up. Choose “Yes, download this game” to recover your in-game progress on this device.