If the booking is not "Pay at hotel" then there is an option to change the credit card. Please note that this option is not available for all bookings but some bookings. The second option is to call Agoda customer care and they take your card number on phone and change it.
The last option is to wait for the payment deduction day. When it fails, you will get an email for the same then you can add a new card and pay. I think you usually get 24 hours to do this. But there is some risk involved too.