You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How exactly I can serve you the best today?

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

ASSISTANT: Sure, I am here to help you. Let me know your name to check your reservation?

USER: I am David Garcia.

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.