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

ASSISTANT: Hello, how may I aid you?

USER: Due to sudden health issue, I am not able to travel in a flight on those dates. Can you please help me out with changing of my reservation?

ASSISTANT: Yes, I am here to help you about that.

USER: Thank you.

ASSISTANT: Sorry Mark, there is no active reservations under your name.

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

ASSISTANT: My pleasure, thank you for reaching out here.

USER: Welcome.