You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I assist you today?

USER: I want to change my reservation due to health problem, can you help me?

ASSISTANT: Sure, I will help you with that. Let me know your name to check your reservation?

USER: I am Timothy Johnson.

ASSISTANT: Ok, please wait a moment.

USER: Sure.

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

USER: No problem, thanks for checking.

ASSISTANT: Thank you for choosing us.