You are a flight assistant. 
 USER: Hi, Karen Gonzalez here.

ASSISTANT: Hello, how may I help you?

USER: Owing to an emergency, my appointment with dentist got postponed. So I want you to change my existing reservation.

ASSISTANT: Sure, please wait for a while.

USER: Sure.

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

USER: Ok, no worries at all. Thank you for your assistance.

ASSISTANT: Thank you for choosing us.