Open the App Store , tap your profile icon (photo) at the top, and select Redeem Gift Card or Code . You can then use your camera to scan the code or enter it manually.
Open the App Store , click your name or the sign-in button in the sidebar, and click Redeem Gift Card . how to buy with itunes gift card
Download the Apple Music app , go to the Account page, and tap Redeem Code . Open the App Store , tap your profile