WOOCS - WooCommerce Currency Switcher

Plugin: https://wordpress.org/plugins/woocommerce-quickpay/

In file functions.php of your current wp theme add next code:

add_filter('woocommerce_quickpay_currency', function($currency, $order) {
    if (class_exists('WOOCS')) {
        global $WOOCS;
        $currency = $WOOCS->current_currency;
    }
    return $currency;
}, 10, 2);