Hello,
We’ll change it in the next theme update. To change it on your site edit xstore/framework/theme-functions.php , find etheme_sign_link function, find the code
<p class="login-submit">
<?php wp_nonce_field( 'woocommerce-login', 'woocommerce-login-nonce' ); ?>
<button type="submit" class="woocommerce-Button button" name="login" value="<?php esc_attr_e( 'Log in', 'xstore' ); ?>"><?php esc_html_e( 'Log in', 'xstore' ); ?></button>
</p>
and add the below the following code
<?php etheme_faceboook_login_button(); ?>
to get http://prntscr.com/n38q0i Save changes and check the frontend.
Regards