change the credit card the subscription is charged

The primary card in your Apple ID account will always be the card used, so just update the card for the iTunes & App Store→If you need to change or update your Apple ID payment method - Apple Support

You can change the payment method associated with your Apple ID by opening Settings ➡️ Apple ID (Your Name at Top) ➡️ Payment & Shipping ➡️ Add Payment Method: Here, add your new credit card first. After it has been added then you can tap on the previous credit card and choose Remove Payment Method.

Axel F.