Don't worry, we have you covered!
First, check that you are signed into Play Games/Game Center, by opening up the game's settings menu and looking for the sign in button (to the left of 'contact us'). If you are not already signed in, tapping on this should load up your previous data.
For Google Play users - If the sign in button isn't there, try signing out of and then back into your Google Play account. This can sometimes give the system the boost it needs to connect and bring your data back across to the game.
Lastly, make sure that your Google Play Games and Google Play Services apps are up to date!
If that doesn't work, please contact our customer support and they can help you out! Tap the 'contact us' button at the top-right of this menu.