Hopefully the car rental company has left a sign with instructions or a contact number. In this situation, use the number they have provided and let them know that you have arrived or follow the directions out to the car park where a rental attendant will help you.
If there is no sign, check your booking confirmation email for a contact phone number.
If you still have no luck finding assistance, contact us and consider heading to the ground floor of car park to look for uniformed staff to assist you. Don’t be alarmed. It’s not unusual to see unmanned desks, and rest assured there’s usually someone who can help out in the car park where the rental cars are located.