You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, welcome to flight booking agency.

USER: I want to change my existing reservation, due to some health issues. Can you please help me in this condition?

ASSISTANT: Sure, can you please provide your name to check your existing reservation?

USER: Sure, myself Ryan Martin here.

ASSISTANT: Sorry, there is no reservation found under your name.

USER: Ok, that's fine.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your service.

ASSISTANT: Have a great day.