You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Matthew Walker.

ASSISTANT: How can I assist you today?

USER: I would like to change my existing reservation which I have done with wrong dates. Can you please aid me to change my existing reservation?

ASSISTANT: Your reservation is found. Will you mention your travelling dates please?

USER: My travelling dates are 10/18 and 10/20.

ASSISTANT: Please mention your airport codes that you want to travel.

USER: My source airport code is SFO and destination code is IAD.

ASSISTANT: Please give me a moment. There is no flights found under your preferable details.

USER: Not an issue, anyway thank you for the information.

ASSISTANT: My pleasure, have a great day.