Apple App icon missing

Go to this link - Redeem your App Store & iTunes Gift Card and if you have trouble go to this one - iTunes - Official Apple Support

Hi Bevvygale! If you need to redeem an Apple Gift Card, you can do so in the iTunes app. Swipe down while in the iTunes app, and select "Redeem". Then, enter your gift card code or scan the barcode, and it should add to your Apple Balance. If you bought an Apple Gift Card, it will add to your Apple Balance. If you bought an iTunes or App Store gift card, they will be added to each balance respectfully. If you are having trouble setting up an Apple Pay Card (Apple Card), go to the Wallet app, select "Enroll in Apple Pay", and follow the onscreen instructions.