You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Nicholas Allen.

ASSISTANT: How can I assist you?

USER: I would like to change my travelling dates, so can you help me for changing an existing reservation?

ASSISTANT: Sure Allen, please wait a moment.

USER: Ok, I will wait for your response.

ASSISTANT: Sorry to say that, there is no reservation found on your name.

USER: Oh! It's ok, no problem.

ASSISTANT: Thank you for approaching us.

USER: Most welcome.