When making an in-app purchase through Apple's App Store or iTunes, you may view this article for instructions on how to update your payment method, and tap here to access your iTunes account settings.
Or follow these steps:
Open the Settings app.> Tap your name > Tap Payment & Shipping.
You might be asked to sign in with your Apple ID.
- To add a payment method, tap Add Payment Method.
- To update a payment method, tap the payment method, then edit your information.
- To remove a payment method, tap Edit, then tap the Delete button.