Hello eyesdrops,
Thanks for using the Apple Support Communities! We understand that you may be having some troubles editting your payment information on your device. Let’s take a look and see what we can do. We're happy to help!
Let's first take a look at this resource that we were able to gather. Let's follow this resource to verify your credit card information in "Settings" under "Wallet & Apple Pay."
Manage the cards that you use with Apple Pay
Next, if you continue to have troubles, let's follow this resource on editing your payment method. Under "If you can't edit your payment information" it states to make sure your device is fully up-to-date on software. If there is an update available, please make sure you backup your device prior to performing any software updates.
Change, add, or remove Apple ID payment methods
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Have a great day!