You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I guide you today?

USER: I want to do some changes in my existing reservation. Can you help  me for that?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: May I know your name please?

USER: My name is Dennis Williams.

ASSISTANT: I found a reservation for you, can you please share your preferable journey dates?

USER: My travelling dates are Nov 21 and Nov 23.

ASSISTANT: Can you please share your source and destination airport codes?

USER: My travelling airport codes IAD and SFO.

ASSISTANT: Do you have any connection limit?

USER: I need a single connecting flight.

ASSISTANT: I am sorry to say that there is no reservation found under your name.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.

USER: Welcome.