You can use the Airbnb gift card purchased online or in store at any time via your desktop, mobile browser, iOS app, or Android app. To do it via the desktop or mobile browser, navigate to “Gift cards” at the bottom menu, click “Redeem”, follow the on-screen prompts to enter your redeeming info, and click “Redeem gift card”.
To use an Airbnb gift card via iOS or Android app, tap “Profile”, choose “Payments & payouts”, navigate to “Credits & coupons”, and tap “Redeem gift card”.