You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: I am Melissa Green. I want to change an existing reservation.Can you help me?

ASSISTANT: Sure Melissa,wait for a moment to check it?

USER: OK.

ASSISTANT: Thank you for waiting. sorry, that I could found a reservation on requested name .

USER: May I know my flight details?

ASSISTANT: Sorry, there is no reservation found Melissa.

USER: OK, thank you.

ASSISTANT: Thank you . Have a good day.