In order to send a reminder email to your participants you must select the 'Email Reminders' tab.
You must then select the radio button which says 'Send reminder email 24 hours before event'
You will then be given a text field in which we have pre populated message to your participants. This is editable, so feel free to input information which will be relevant to people attending your Open Day.
Once you have done this, don't forget to 'Save Changes' at the bottom of the page.