You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Margaret Lopez.

ASSISTANT: How may I assist you?

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

ASSISTANT: Ok, please wait a moment.

USER: Sure, take your own time.

ASSISTANT: Thanks for your time, there is no reservation under your name.

USER: That's fine.

ASSISTANT: Ok, thanks for choosing us.

USER: Thank you for your help.