Select Tools –> Global Check-in from the drop-down menu on the Back-end of your Joomla! installation.
Description
Selecting this menu option causes Joomla! to perform a global check-in of all checked out or locked items. It then shows the results of the Global Check-in. This is useful, for example, if an Articles is locked by a User who opened it for editing and never finished the editing session. In this case, other Users are not able to edit this Article. Performing a Global Check-in releases all such items.
Screenshot
Works for all Joomla versions