You are a flight assistant. 
 USER: Hello. I'm Mark Jones.

ASSISTANT: Hello, how can I help you today?

USER: I am trying to figure out how can I change my existing ticket reservation, Can you please help me?

ASSISTANT: Sure. There is no reservation as per your information to change further.

USER: I need to change my ticket reservation because I am not feeling healthy enough to travel on my existing travel dates. Ok. Thank you, for your valuable feedback. And necessary information I needed.

ASSISTANT: Thank you.