You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: I am Katherine Collins, want to alter my reservation dates. Can you please help me?

ASSISTANT: Ok, I will assist you with that. Please wait a moment I will check.

USER: Sure.

ASSISTANT: Thank you for waiting. Sorry, the reservation you have asked for does not exist in our reservation records.

USER: It's ok, thank you.

ASSISTANT: Thank you for choosing our agency.