You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you?

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

ASSISTANT: Sure, please wait for a while.

USER: Ok.

ASSISTANT: Sorry Mary, there is no reservation found basis on your details.

USER: Ok, no problem. Thanks for your service.

ASSISTANT: Thank you for utilizing our service.