You can't do anything to that reservation since the member who used their points to make the reservation still owns it. They have to add it at least 48 hours before and it must be paid for when added. So you'll have to find a way to pay the member to add it.
You could ask the member to do a three way call in which you would provide your credit card info to MS. The card holder has to be some one on teh reservation. Of course this also means that the member will hear your card data as well.