You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you today.

USER: Could you please change my existing reservation due to my health issue?

ASSISTANT: Let me know your name to check your reservation?

USER: I am Frank Campbell.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

ASSISTANT: Thank you for waiting.

USER: Not a problem, thank you.

ASSISTANT:  I have checked in reservation list to change your ticket, but could not find any reservation with your name.

USER: Thank you.

ASSISTANT: Thank you for choosing us.