Hello.
user
Hello, how may I aid you?
assistant
Can you please help me in  change my existing reservation?
user
Sure, may I know your name?
assistant
Myself David Clark.
user
Please give me a moment to check your ticket status.
assistant
Sure.
user
Sorry David Clark, no reservation is available by your name.
assistant
Not a big deal, anyhow thank you very much for your information.
user
Thank you for choosing us.
assistant