Gather any notes and drafts you can find, to show you worked on the assignment. You can send them to the Academic Conduct Officer (ACO) before the meeting or bring it with you if you're meeting in person. You may also still have the websites you visited in your browser history, which could show you visited the sources at the time.
Go through your essay and remind yourself of the topic. Be prepared to answer specific questions about what you wrote - think of it as an oral exam where you explain your work. Think about the sources you used, how you found them, and why you decided to use them. Which sources did you find particularly useful?
If your work is very different than your other assessments, did you approach it differently this time? Did you understand this topic more, put more effort into it, or have you worked hard to improve your skills?
If there are any concerns about file properties, such as the author name, think about how this happened. If you worked on someone else's computer, do you have any evidence? Did you create a new document at the last minute and copy the essay into it?
If you did obtain your work from someone else or get help with it, submit a statement to explain what happened. If there was anything happening in your personal life that was affecting your ability to study, make this clear in your statement and send evidence of those circumstances.