You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Mark Martin.

ASSISTANT: How may I serve you at this moment?

USER: Can you change my existing reservation?

ASSISTANT: Sure, please wait for few minutes.

USER: Sure.

ASSISTANT: There is no existing reservation found on your name in our data base. Thank you for reaching us.

USER: Ok, No issues. Thank you.