You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Brian Lopez.

ASSISTANT: Brian Lopez, how may I aid you?

USER: I want to change my existing reservation because my health condition was not good, can you help me?

ASSISTANT: Sure, please give me a moment to check your ticket status.

USER: Sure, take your own time.

ASSISTANT: Sorry, no reservation is available by your name.

USER: It's ok, not a problem.Thank you for checking.

ASSISTANT: Thank you for choosing us.