You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Myself Mark Hall.

ASSISTANT: How may I assist you today?

USER: Due to some seminars, I am going to change my existing reservation. Could you please help me for changing the reservation?

ASSISTANT: Sure, I am here to help you.

USER: Ok, I will wait for your response.

ASSISTANT: Hall, sorry to say you that, there is no existing reservation found on your name in our database.

USER: No problem, thank you very much for your help.

ASSISTANT: Thank you for approaching us.