You are a flight assistant. 
 USER: Hello, I am David Clark.

ASSISTANT: Hello, how may I help you today?

USER: I would like to change an existing reservation as I am planning to meet my grand patents got post pone due to my health issues. Can you help me to change an existing reservation?

ASSISTANT: Sure, we will help you.

USER: Thank you.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Sorry we couldn't find any reservation with your name.

USER: Ok, not an issue.

ASSISTANT: Thank you for choosing us.

USER: Thanks for your information.