Immediately after joining S.RIDE Premium, you may not be able to select the car type at the time of reservation dispatch, which is a privilege.
In this case, please try the following.
・ Press "Reserve" at the bottom of the screen. Next, press the "←" button displayed at the bottom left of the map screen to return to the reservation time selection screen and try the reservation dispatch again.
・ If the above does not improve, close the S.RIDE app once and start it again to select the car type normally.