Inside the XML file add :

<field name="link" type="menuitem" default="" label="FEATURES_LINK_LABEL" description="FEATURES_LINK_DESC" rows="5" cols="40" required="1" />

Inside the PHP, call the Itemid

 <?php if($helper->get('link')) : ?>
                    <?php $idMenu = $helper->get('link'); $active = ($idMenu == $id_active) ? "active" : ""; ?>
                    
			<a href="/<?php  echo JRoute::_("index.php?Itemid={$idMenu}"); ?>" title="" class="features-link <?php echo $active;?>">
                <?php endif ; ?>
                
				<?php echo $helper->get('ft-title') ;?>
			</a>

Or, if it's boucle 

<?php if($helper->get('link', $i)) : ?>
<?php $idMenu = $helper->get('link', $i); $active = ($idMenu == $id_active) ? "active" : ""; ?>

<a href="/<?php  echo JRoute::_("index.php?Itemid={$idMenu}"); ?>" class="features-link <?php echo $active;?>">
<?php endif ; ?>


<?php if($helper->get('title', $i)) : ?>
<h4><?php echo $helper->get('title', $i) ?></h4>
<?php endif ; ?>

</a>