When you open your menu in-game (bottom left), you will see a pop-up that says 50 free dice, connect. If you choose to interact with this button you will be redirected to log in to your Facebook account. If the login is successful, the pop-up will close and you will receive your bonus rolls. Another way to connect your Facebook account is to select the more button when you go to attack. This drop-down menu will give you the option to link your Facebook account and receive 50 free dice.