If a previous employee returns to work at your company, you can reinstate them on Polaris.
This can be done by finding the employees record on staff maintenance - you can view leavers by choosing "Only Leavers" or "Include Leavers" on the Show Leavers drop down section.
Once you have found the leaver in question - navigate your way to the leavers tab in their staff maintenance (the aeroplane symbol).
Once on this tab, click "Re-Employ", then confirm "Yes, re-employ" on the pop-up screen and you will be able to reinstate the employee.
Once this is done, all their personal data will be repopulated, except job type and pay rate which will need to be added - this is because they may be coming back to do a different job to what they were originally.