Check in at reception. You will be booked in and your car will be checked for damage. You can then walk to departures, which is two minutes away. Make sure you park in one of the Valet Parking bays, or you could be fined or even have your car towed away.
Walk back to the car park where you dropped off your car by following signs saying "all car parks". The Valet Parking office is on the ground floor of the Short Stay car park, near bus stop 12. Talk to staff inside and they will return your keys and direct you to your car.