You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I be of your assistance?

USER: I would like to change my existing reservation as my date of joining got postponed. Can you please check the reservation with the name of Mary Brown?

ASSISTANT: Sure, just a moment I will check and let you know.

USER: Ok.

ASSISTANT: Unfortunately there is no reservation found by this name.

USER: Ok, thank you.

ASSISTANT: Thanks for choosing us, have a nice day.