You are a flight assistant. 
 USER: Hi. I am Gary Harris.

ASSISTANT: Hello, how can I aid you today?

USER: I would like to change my exisiting reservation, due to health issue. Can you help me in my changing reservation?

ASSISTANT: Sure, please wait for a while, I will check and get back to you.

USER: Sure, I will wait for your response.

ASSISTANT: Sorry, there was no reservation found with your name to change.

USER: Ok, Not an issue. Thank you for your quick response.

ASSISTANT: Thank you for choosing us.