When creating a new Group Event, you may see the option to 'Link to Attendees' when you are Copying From another set of dates.

What does this mean?

This option will show if the term/date you are copying from had bookings on it.

If you tick 'Yes', Book That In will be able to send an email to all those Attendees who were booked onto the previous term/date with a link to book the new one you are creating.

Once you have created the new date block, you will see a button on the Group Overview display, saying 'Send Notification Emails', plus the option to edit the email prior to sending it. 

Click the button to send the email out to all attendees on the previous block.

If you are creating the term/date in advance, you can opt to send the notification email later if you want.