Here's how to sync your game so that you're able to recover it whenever you install the game.
On Google (In-game):
In Earth Wars, Tap 'Menu' on your base, then Tap 'Settings' and then Tap 'Account' in the navigation. Once you are there, tap the 'LOGIN' button > 'Confirm'.
On Apple (Out of game):
Tap 'Settings' > 'Game Center', and then 'Sign in'.
To clarify, we cannot change already established syncs and you must contact Apple (https://support.apple.com/en-gb/HT204921c) or Google Support (https://about.google/contact-google/) for assistance in restoring your accounts.