If you would like to view your current Facebook balance, go to the Payments tab of your account Settings.
In order to use your existing local currency balance in your desired game, please follow the steps listed below:
- Open up the app you want to use your account balance in.
- Select the in-game currency package or item you would like to purchase.
- Click Continue.
- If you have a sufficient account balance to make the purchase, click Buy to complete it.
- If your account balance is insufficient to make your purchase, you will see how many additional funds you need in order to complete the purchase. Select which payment method you would like to and complete the transaction by clicking the Buy button.
See here for more details.