the credit card on applepay has expired..how do i enter the new expiry date?

I have never had to update the expiration date on an Apple Pay credit card. See the following from Manage the cards that you use with Apple Pay - Apple Support

While you can't change your card number or expiration date, it should update automatically when you get a new card. If your issuer doesn't support updates, you might need to remove the card, then add it again.