@Yogesh
Hm, try this. Go to same file.
Find code that is very similar to this (may not exactly match):
<div class="elem regdate">
<?php if(osc_item_user_id() <> 0) { ?>
<?php echo __('Registered on', 'zara') . ' ' . osc_format_date( osc_user_reg_date() ); ?>
<?php } else { ?>
<?php echo __('Unregistered user', 'zara'); ?>
<?php } ?>
</div>
Replace it with:
<div class="elem regdate">
<?php if(osc_item_user_id() <> 0) { ?>
<?php $get_user = User::newInstance()->findByPrimaryKey( osc_item_user_id() ); ?>
<?php if(isset($get_user['dt_reg_date']) AND $get_user['dt_reg_date'] <> '') { ?>
<?php echo __('Registered on', 'zara') . ' ' . osc_format_date( $get_user['dt_reg_date'] ); ?>
<?php } else { ?>
<?php echo __('Unknown registration date', 'zara'); ?>
<?php } ?>
<?php } else { ?>
<?php echo __('Unregistered user', 'zara'); ?>
<?php } ?>
</div>