If there is a specific person you would like to invite back to re-register you can do this without inviting the entire database. To do this, go to Online Registrations > click on the name of the database to display a list of all people registered > find the person eg. George Barker > then click the envelope icon beside their name >
This opens up the dialogue box showing it will only email George Barker. You can then personalise the message and click Confirm to send the email invite.