change my subscription payment to Discovery Plus from my Apple Store account to my credit card?

Greetings MnTommy,

You can learn how to edit your payment methods for your Apple ID here:

If you need to change or update your Apple ID payment method - Apple Support

"Update your payment method on your Mac

1. Open the App Store.
2. Click your name or the Sign In button.
3. Click Account Settings.
4. Next to Payment Information, click Manage Payments. (If you're using an older version of macOS, click Edit next to Payment Type.)
5. Click Add Payment, then enter the new payment method. Click Done.

       6. Click Edit next to the old payment method, then click Remove Payment Method."

Take care.