You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: William Perez here.

ASSISTANT: William Perez, how may I render you?

USER: Can you please help me with changing my previous booking at this moment?

ASSISTANT: Sure, please give me a moment to check your ticket status.

USER: Ok, take your time.

ASSISTANT: Sorry, no reservation is available by your name.

USER: Oh! That's fine. Thank you for checking anyways.

ASSISTANT: Thank you for reaching us.

USER: Welcome.