I filed a complaint he EEOC and I have a meeting scheduled in three days. Do I tell my HR department or will they?

In the absence of other information, I would say do not inform your employer. At this point, the only exception that occurs to me is if you are a federal employee and the time for you to meet with an equal employment opportunity counselor would expire within the next few days. Good luck to you.

I am not sure what meeting you are talking about. If you filed your charge, the EEOC will notify your employer of the charge. If you are scheduling a mediation, the EEOC will schedule it with both you and your employer. If you mean that you scheduled an appointment to file a charge at the EEOC and that appointment is during business hours, you will need to take a personal day and notify your employer that you cannot go to work during that time, though you likely do not want to share the fact that you will be filing a charge.