HI!

in the:

/wp-content/themes/thegem/top_area.php

instad of (line 18)

<?php thegem_button(array('href' => thegem_get_option('top_area_button_link'), 'text' => thegem_get_option('top_area_button_text'), 'size' => 'tiny',  'no-uppercase' => true), true); ?>

Add this code

<a class="gem-button gem-button-size-tiny gem-button-style-flat gem-button-text-weight-normal gem-button-no-uppercase" href="http://link,com" target="_blank">test</a>

it's template just copy it to the child theme.

Or add 

'target' => '_blank',  

after

'size' => 'tiny',

on line 18