You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I guide you?

USER: Could you please help me to change an existing reservation as my plan to meet my grand parents got postpone due to my health issues?

ASSISTANT: Sure, We are here to assist you. May I know your name?

USER: I am David Hall.

ASSISTANT: Please wait a while.

USER: Sure.

ASSISTANT:  Thank you for waiting, but I am sorry to say that, there is no active reservation found with your name in our database to change it.

USER: Ok, not an issue. Thank you for your information.

ASSISTANT: Thank you for reaching us.