owno
I assume that you're setting to show created date for articles, you can open this file:
/templates/buildr/html/layouts/joomla/content/info_block/create_date.php
then see this line of code:
<?php echo JText::sprintf( JHtml::_('date', $displayData['item']->created, JText::_('m-d-y'))); ?>
change the date formate as you wish: m-d-y
Check out this reference for more info about date formate: https://www.php.net/manual/en/function.date.php
In case you're showing published date, you can edit the same way in this file: /templates/buildr/html/layouts/joomla/content/info_block/publish_date.php