You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Brenda Williams.

ASSISTANT: What can I do for you?

USER: I would like to travel Austin for giving a seminar at my friends office, can you please help me in booking a ticket?

ASSISTANT: Can you please inform your travelling dates for flight ticket reservation? Can you please mention source and destination airport codes?

USER: I have already done with my reservation, but I want to change my existing reservation, can you please help me with this?

ASSISTANT: Sure, please wait a moment. There is no reservation found on your name. There is no reservation found on your name Brenda Williams.

USER: No problem, thank you for checking.

ASSISTANT: Thank you for approaching us.