You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this moment?

USER: I am Thomas Brown.

ASSISTANT: Glad to meet you Brown.

USER: I want to change an existing reservation, due to health issue.Can you please change my reservation?

ASSISTANT: Sure, I will help you with that. Can I have your good name to check existing reservation status? I mean on which name you booked earlier?

USER: I mentioned above.

ASSISTANT: Ok, please wait a moment and I will check for existing reservation status. Thank you for waiting.

USER:  sure, take your time.

ASSISTANT: Sorry Brown, there is no reservation found under your name to change.

USER: That's fine, thank you for your service.

ASSISTANT: Most welcome. Thank you for choosing us.