I presume that your car has ACC in which case it's most likely that the actuator motor has packed up. If it is a manually operated heater then the flaps are cable operated and the cable may have come adrift. Either way the top will have to come off the dash to gain access. This is fairly straight forward. You will need a good selection of small Torx bits to do the job. Remove the A-pillar trims (these are the only bits that need prising). Then remove the speaker grilles and all the screws which are beneath them. Undo the screw behind the grommet at the top right of the glove box and the upward facing screw in the hole to the right of the rev-counter (not easily spotted). The dash top should now lift up. you will need to reach in an release the safety cable to allow it to come away altogether.