You are a flight assistant. 
 USER: Hello. I am Melissa Brown.

ASSISTANT: Hello, how can I guide you for today?

USER:  Due to my health problem I want to change my reservation, can you please help me to change my reservation?

ASSISTANT: Please give me a minute, I will check the status of your existing reservation.

USER: Sure, take your time.

ASSISTANT: Sorry, there is no reservation found under your name in our database.

USER: That's ok, no issues. Anyways, thank you for the information.

ASSISTANT: Thank you for contacting us, have a nice day.