You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Donald Baker.

ASSISTANT: How may I support you today?

USER: Due to some sudden changes i want to change my existing reservation. Can you help me?

ASSISTANT: Sure, please wait a moment i will check the reservation list.

USER: Ok.

ASSISTANT: Thanks for waiting, unfortunately there is no reservation found by this name.

USER: It's Ok, thanks for your response.

ASSISTANT: Thanks for availing us.