To achieve this please add following custom code in the bottom of functions.php file of child theme that you are using on your site.

function add_pricing_button_custom_scripts(){ ?>
	<script type="text/javascript">
		jQuery(document).ready(function($){
			$("#page-container .sh-pricing-content-center a.sh-pricing-butto").attr("target","_blank");
		});
	</script>
<?php }
add_action('wp_footer', 'add_pricing_button_custom_scripts', 99);