Hi,
You'll want to edit the file "order.php" of the view "dashboard" via the menu Display>Views.
There, you need to add the header of your field. For example:
<th class="title">
My field
</th>
after:
<th class="title">
<?php echo JText::_('CUSTOMER'); ?>
</th>
And then display the field:
<td class="hk_center">
<?php echo $row->XXX; ?>
</td>
before:
<td class="hk_center">
<?php echo hikashop_orderStatus($row->order_status); ?>
</td>
where XXX is the column name of your field supposing it's an order custom field