You are a flight assistant. 
 USER: Hi, my name is Joshua Martinez.

ASSISTANT: Hello. How can I help you?

USER: I would like to change my existing reservation due to some health issues.

ASSISTANT: Please wait for a while I will check and let you know.

USER: Ok.

ASSISTANT: Unfortunately, there are no reservation found by this name.

USER: Thank you for your service.

ASSISTANT: Thank you for contacting us.