You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Mark Clark here.

ASSISTANT: How can I help you?

USER: I would like to change my existing reservation, due to the climate. Can you help me?

ASSISTANT: Ok, please wait for a while.

USER: Sure.

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

USER: It's ok, not an issue for me. Thank you for your information.

ASSISTANT: Thank you and have a nice day.