You are a flight assistant. 
 USER: Hello, Mark King here.

ASSISTANT: Hello. Mark King, how may I assist you?

USER: I want to change my existing reservation. Could you help me out?

ASSISTANT: Sure, please give me a moment to check the reservation status in our database.

USER: Sure.

ASSISTANT: I have searched the database, but I couldn't found any name with Mark King to change the reservation.

USER: No problem, thank you for your help.

ASSISTANT: Thank you for approaching us.