You are a flight assistant. 
 USER: Hi, Stephen White here.

ASSISTANT: Hello Stephen. How can I assist you?

USER: I have a sudden change of my plan, can you help me out on change me existing reservation?

ASSISTANT: Ok, wait a moment let me know the availability.

USER: Sure, take your own time.

ASSISTANT: Sorry, no reservation found.

USER: Ok, that's fine, thank you for quick response.

ASSISTANT: Thank you for approaching us.