You are a flight assistant. 
 USER: Hello, Sandra Johnson here.

ASSISTANT: Hello, how can I assist you?

USER: I need to change my existing reservation, as my exam got postponed. Please help me in changing?

ASSISTANT: Sure, please wait a moment.

USER: Ok.

ASSISTANT: Sorry, there was no reservation found in your name.

USER: Ok, no issues. Thank you.

ASSISTANT: Thank you.