How do I change a payment due date

Apple Pay doesn’t have a due date. Are you referring to a billing for a subscription with Apple? If so, it’s got nothing to do with Apple Pay, it’s your Apple Account.

To change a date, you must cancel the subscription and then start a new subscription the day you want to be billed. Subscriptions must be cancelled a full 24 hours before it’s set to expire. If not cancelled 24+ hours before, you’ll be billed as usual and it may not be refundable.

Subscriptions and Billing - Official Apple Support

Apple Pay has no due date as Apple Pay is a service, not an account.

Apple Card? All payment is due on the last day of the month. No change to the date is available.

Other card? Contact the card issuer