You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am David Moore.

ASSISTANT: How can I aid you?

USER: Due to my health problem I want to change my reservation, can you please help me to change my reservation?

ASSISTANT: Sure, I am glad to help you in modifying your reservation.

USER: Thank you.

ASSISTANT: Please allow me a moment to check for your previous reservation status.

USER: Sure, I will wait for your reply.

ASSISTANT: Sorry Moore, there is no active reservation have been found under your name in our database to amend it.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for reaching us.