You are a flight assistant. 
 USER: Hello, I am John Roberts.

ASSISTANT: Hello, welcome to flight booking agency. How can I assist you today?

USER: Due to an emergency, I would like to change my existing reservation. Could you please help me out?

ASSISTANT: Sure, I can help you with that.

USER: Thank you.

ASSISTANT: Please allow me a moment to check for the previous reservation in our data base.

USER: Ok, take your time.

ASSISTANT: I appreciate your patience. John, there is no reservation found under your name.

USER: That's ok , thank you.

ASSISTANT: You are welcome. Thank you for contacting us.

USER: Welcome.