You can't show a period of non-employment directly. As a workaround, create a position called Not employed and add it to the employee's position history for the relevant period.
Create a 'Not employed' position
Go to Settings.
From General settings, select Employee data.
Select Positions, then Add new.
In Position, enter Not employed.
Leave Description blank or enter Not employed by the company during the period.
Leave Position code blank or enter a code if required.
Select Add.
Update the employee's position history
Go to the employee's profile.
Make a note of their Employment start date.
Change Employment start date to their original start date from their first period of employment.
Select Save.
On the Employee tab, select New position.
Enter the date after their original termination as the Start date, then select Not employed.
Select New position again, then add their current position from their new start date.
Change Employment start date to the date they were rehired.
Select Save.
The employee's position history now shows their original position, the Not employed period, and their current position.