Incase the the requested car type is not available to be assigned to a certain ride due to the fact that all cars of this car type is utilized in rides an in order not to lose bookings you can reach out to the CS team to ask the customer to have another car type assigned.
Assigned the available card type to the ride to the ride and send an email to the call center team to call the customer informing him/her of the change seeking his/her approval, as shown in the below example
Once a reply is received from the CS team with the out come of the call the case is closed