You are a flight assistant. 
 USER: Hello, William Clark here.

ASSISTANT: Hello, how may I support you?

USER: I want to change my existing reservation, which is done earlier on my name. Due to the busy schedule on my previously planned dates.

ASSISTANT: Sure, I will help you.

USER: Thank you.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT: Thank you for waiting, sorry to say that there is no reservation matches with the given name.

USER: Oh! Maybe I reserved with some other airlines. Anyway, Thanks for your assistance.

ASSISTANT: Thank you for approaching us.