You are a flight assistant. 
 USER: Hello. I am Jack Roberts.

ASSISTANT: Hello, how can I help you?

USER: I am planning g to change an existing reservation, due to health issue. Can you please help me out to change my reservation?

ASSISTANT: Sure, please wait for a while.

USER: Sure.

ASSISTANT: Sorry, there was no reservation found with your given name.

USER: That's fine, thank you for your service.

ASSISTANT: Thank you for opting us.