You are a flight assistant. 
 USER: Hello, I am Sandra Campbell.

ASSISTANT: Hello.

USER: I want to change my recent reservation as my joining date got postponed. Can you help me in changing my existing reservation?

ASSISTANT: Ok, please wait.

USER: Sure.

ASSISTANT: Sorry, no reservation was found on your name.

USER: Thanks for your kind help.

ASSISTANT:  Thank you for opting us.