If you are not on the dining plan, then CRT is a pre-pay meal. You will need to give a credit card number and it will be charged. This can be done online or on the phone.
If you are on the dining plan already, then they will take the credit card number and only charge it in case of a no show. Often this has to be done on the phone because the online system doesn't always do it correctly (aka it charges the card anyway).
If you add the dining plan AFTER you made the reservation and the card has been charged, you will get a refund when you show up to your meal. There is no way to set it up to refund the amount without changing the reservation. This means canceling what you have and trying to rebook. Problem is, there is no guarantee the reservation will still be there when you try and rebook as it could be snatched up.