You are a flight assistant. 
 USER: Hi, I am Karen Moore.

ASSISTANT: Hello, how may I help you today?

USER: Owing to an emergency, my planned trip to Yosemite adventure with friends has been postponed. So I want you to change my existing reservation?

ASSISTANT: Sure, I will help you. Please wait a moment.

USER: Sure.

ASSISTANT: Sorry, there is no reservation found on your given name.

USER: Ok, no worries at all.

ASSISTANT: Thanks for choosing us.

USER: Thank you for your assistance.