If you really did it properly, they wouldn't. However, I doubt you have any idea how AI checkers work, and much less have any idea how to get around them. Frankly it would actually end up being more effort than if you had written the whole thing yourself, not to mention less stressful since you wouldn't have to worry about being caught and disqualified for using AI. Its honestly not worth the trouble. Instead, use AI to help you structure, rephrase and find sources for your EPQ. This is a perfectly reasonable use of AI and will not get you in any trouble. Not to mention it will cut your time investment significantly.
It's also my obligation to mention why using AI is a bad idea. The entire point of writing an EPQ is to give you an opportunity to independently learn research skills, learn how to put together a piece of research, how to present an argument, and how to effectively manage your time. By using AI to do the bulk of the research and writing, you are outsourcing these tasks and thereby completely missing the point of the EPQ. You might as well not do the EPQ at all. The time you spend 'going over and rephrasing it so you become familiar with it' would effectively be a complete waste of your time, time which you could have spent revising or doing literally anything else. Actually writing the EPQ, on the other hand, would not be a waste.