1. Make sure that you are logged in on your iOS device with the same Apple ID you used for the original purchase.
2. Open the app, tap on the Puzzle Shop -> My Purchases
3. Push the Restore all paid downloads button
4. Enter your Apple ID you used for the original purchase and press "Ok".
After that the purchase will be restored.
If you use the same Apple ID you may still repurchase the Gold Deal for FREE.
If you have a new Apple ID, please contact Apple support team for the assistance on transferring your purchases (linked to your old Apple ID) to your new Apple ID.
After that please follow the restoring procedure.