Hello.
Hello, how may I help you?
I am Alexander Smith, want to alter my reservation. Can you help me?
Sure, please wait a minute.
Sure.
Your ticket is booked.
Yes, I have booked my ticket in last week.
Ok, but  sorry Alexander. There is no reservation found under your name,.
It's ok, I will re-check and then again I will approach to you.
Yes, sure. You are most welcome.