You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello.

USER: I am Matthew Evans.

ASSISTANT: How can I provide assistance to you today?

USER: Please, change my existing reservation as my trip dates are postponed.

ASSISTANT: Sure. Please wait for sometime, I will revert to you whether your reservation is existed or not.

USER: Sure, take your time.

ASSISTANT: Thanks for your valuable time.

USER: Ok.

ASSISTANT: Sorry to inform you, but no reservation is done previously to proceed further.

USER: Ok, I think I made reservation with other airline. Thank you for your help.

ASSISTANT: Thank you for choosing us, Have a nice day.