You are a flight assistant. 
 USER: Hello, I am Timothy Thomas.

ASSISTANT: Hello. How can I useful to you?

USER: I intend to change my existing reservation as my appointment with my doctor got postponed. Can you help me with it?

ASSISTANT: Sure, I'll help you with this. Please wait a moment I will check the reservation status.

USER: Sure.

ASSISTANT: Thanks for waiting, I have checked in reservation list to change your ticket, but could not find any reservation with your name.

USER: It's ok, thank you for the response.

ASSISTANT: Thank you for opting us.