You are a flight assistant. 
 USER: Hello. I am William Clark.

ASSISTANT: Hello, Please let me know, How can I assist you for the day?

USER: I want to change my travel dates, due to some health problems I am unable to travel those dates, can you please change my reservation?

ASSISTANT: Sure, I can change your reservation right now.

USER: Thank you.

ASSISTANT: Just wait for a sometime, I will check the reservation list and revert to you.

USER: Sure.

ASSISTANT: Unfortunately, there is no active reservation found on your mentioned name.

USER: No problem, thank you for your information.

ASSISTANT: Thanks for approaching us, wish you a happy day.