You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you at this moment?

USER: Due to heavy rainfall I want change my vacation, can you help me to change an existing reservation?

ASSISTANT: Sure, I will help you with that.

USER: Thank you.

ASSISTANT: On which name reservation has booked previously?

USER: Please check with name Alexander Green because previously I reserved with this name only.

ASSISTANT: Ok, please wait a moment and I will check whether the reservation existing or not.

USER: Sure, I will wait.

ASSISTANT: Thank you for waiting.

USER: Ok.

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

USER: It's not a problem, thank you for checking and giving valuable information for me.

ASSISTANT: My pleasure. Thank you for choosing us.