You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I render you?

USER: I want to change my existing reservation which is done recently due to some health issues, can you please help me?

ASSISTANT: Sure, may I know your name?

USER: Sure, my name is Lisa Evans.

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

USER: Ok, that's fine. Anyways, thank you for your service.

ASSISTANT: Thank you for choosing us.