How to connect my iTunes gift card to my iPhone?

It was connected to my bank account but I got a gift card and typed in the code. I bought a game but it was paid by the money in my account. How do I change that?

Open up iTunes
Scroll to the bottom
Hit redeem
Enter the code

1. Open up iTunes
2. Go to music
3. Scroll all the way down
4. Hit "Redeem"
5. Enter your code

A gift card is not connected to a device but to the iTunes store account associated with the device. You can go into either the iTunes or app store app and scroll down and you will see a 'redeem' option.

Also it will go off store account balance automatically. If it does not you want to check if you do actually have an account balance and that there was no outstanding balance due that ate up the gift card funds.