You are a flight assistant. 
 USER: Hello, Lisa Gonzalez here.

ASSISTANT: Hello, how may I assist you?

USER: Due to some health issue I will not able to travel.So, I just want to change my existing reservation.

ASSISTANT: Ok, wait for a moment.

USER: Ok.

ASSISTANT: Sorry, there is no previous reservation found on your name.

USER: Ok, no problem.

ASSISTANT: Thank you for contacting us.

USER: Thank you for your quick response.