FOX - WooCommerce Currency Switcher Professional

Plugin URL: https://woocommerce.com/products/extra-fees-for-woocommerce/

To your current child wp theme file functions.php add next code:

add_filter('efw_gateway_fee_after_calculate', function ($fee_value) {

    if (class_exists('WOOCS') AND $fee_value) {
        global $WOOCS;
        $fee_value = $WOOCS->woocs_exchange_value(floatval($fee_value));
    }

    return $fee_value;
});

add_filter('efw_order_fee_after_calculate', function ($fee_value) {

    if (class_exists('WOOCS') AND $fee_value) {
        global $WOOCS;
        $fee_value = $WOOCS->woocs_exchange_value(floatval($fee_value));
    }

    return $fee_value;
});