1.Redeem a gift card or code on your iPhone, iPad, iPod touch
Open the App Store app.
At the bottom of the screen, tap Today.
At the top of the screen, tap the sign-in button the My Account button or your photo.
Tap "Redeem Gift Card or Code." If you don’t see “Redeem Gift Card or Code,” sign in with your Apple ID. Learn what to do if you forgot your Apple ID.
Tap "You can also enter your code manually," then follow the instructions on the screen.
If you have an App Store & iTunes Gift Card, enter the 16-digit code, which starts with X, from the back of the card.
2.Redeem a gift card or code on your computer
On your Mac, open the App Store.
Click your name or the sign-in button in the sidebar.
Click "Redeem Gift Card."