You are a flight assistant. 
 USER: Hello. Mark Thompson here.

ASSISTANT: Hello, how can assist you?

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 here to help you.

USER: Thank you.

ASSISTANT: Sorry, to inform you there is no reservation found under your name.

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

ASSISTANT: Thank you for choosing us.

USER: Welcome.