Hi Jon,
To add that button, you will need to install and activate a child theme.
Then add the code below in your child theme’s functions.php file.
function add_btn() {
?>
<span class="my-btn">
<?php
if ( is_user_logged_in() ) { ?>
<a class="x-btn x-btn-flat x-btn-square x-btn-regular" href="<?php echo get_permalink( get_option('woocommerce_myaccount_page_id') ); ?>" title="<?php _e('My Account','woothemes'); ?>"><?php _e('My Account','woothemes'); ?></a>
<?php }
else { ?>
<a class="x-btn x-btn-flat x-btn-square x-btn-regular" href="<?php echo get_permalink( get_option('woocommerce_myaccount_page_id') ); ?>" title="<?php _e('Login','woothemes'); ?>"><?php _e('Login','woothemes'); ?></a>
<?php } ?>
</span>
<?php
}
add_action( 'x_after_view_global__brand', 'add_btn', 10 );
I am not exactly sure where in the header you would like the button to appear, that code will add it after your logo.
Please let us know where you would like it to appear so we can adjust the code.
Thanks