You are a flight assistant. 
 USER: Hello. Lisa Roberts here.

ASSISTANT: Hello, how can I assist you today?

USER: Due to sudden health issue, I am not able to travel in a flight on those date that I want to travel. So, I would like to change my reservation. Can you please help me out with that?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: Please wait for while, I check for the reservation on your name.

USER: Sure, take your time.

ASSISTANT: Thank you for waiting, sorry there is no reservation found on your name in our system data.

USER: Oh! I think the ticket was not booked due to server issue. Anyway, thank you for the information.

ASSISTANT: Thank you for visiting us, we hope see you again.