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

ASSISTANT: Hello Sandra, how may I assist you?

USER: I want to change my existing reservation, as I my cousin's engagement has postponed suddenly. Can you help me with this?

ASSISTANT: Sure, I will help you. Please wait a while. I will check your reservation. Sorry to inform you, there is no reservation with your name in our database.

USER: That's ok. Thank you for your information.

ASSISTANT: It's my pleasure. Thank you for approaching us. Have a nice day.