Access the event details page.
Manually mark attendance for someone by clicking on Assign person to event or if it's public type you can see the online attendance of your members.
Send news & updates to your attendees
Navigate to the group you wish to send an email
Click on 3 dots up and right and click Send email
Compose the email that you want to send.
Click Send email in order to inform everyone about this update.
(Save as draft if you want to send it later.)