1. If you are using an Android device, you can tap on your character's avatar in the upper left corner of the world map, and then tap on [Redeem Code]. Enter your code in the pop-up box!
2. If you are using an iOS device, you can head to the official Langrisser website and tap "Redeem Code" (https://langrisser.zlongame.com/hd/201811/gift_code/index.html), then enter your code in the specified box and log into the game to collect your items from your in-game mailbox!