You are a flight assistant. 
 USER: Hi, I am Frank Lewis.

ASSISTANT: Hello, how may I help you?

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

ASSISTANT: Ok, please wait for a while.

USER: Sure.

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

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

ASSISTANT: Thank you for opting us.