You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is John Clark.

ASSISTANT: How may I help you out?

USER: I want to do some changes in my existing reservation. Can you help me for that?

ASSISTANT: Sure, I will help you in changing the ticket.

USER: Thank you.

ASSISTANT: Sorry, there are no reservations found.

USER: That's ok, thank you for checking.

ASSISTANT: Thank you for reaching us.

USER: Welcome.