How can I change my due date

You can’t … ALL Apple cards are “due” by the last day of the month.

Excerpt from AppleCard’s Terms & Conditions (accessible from within your wallet):

“… Your payment is due by 11:59 P.M. ET on the last calendar day of each month … “

You’re welcome.

To be clear, AppleCard’s terms seem quite generous.

I’m not aware of any other “major” CCard issuer which allows a full month to make payment after a statement “close out.”