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

ASSISTANT: Hello, how can I aid you for today Mark Phillips?

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: I am here to help you with that.

USER: Thank you.

ASSISTANT: Sorry to say this there is no active reservation with your name to change your reservation.

USER: Oh! Not an issue, thank you for the information.

ASSISTANT: You are welcome, thank you for reaching us.