WooCommerce Checkout Page change Label Text

functions.php

function add_wc_custom_fields($fields) {
global $woocommerce;
    $countries_obj   = new WC_Countries();
    $countries   = $countries_obj->__get('countries');

     $fields['billing']['billing_first_name'] = array(
            'label' => '',
            'placeholder' => _x('First Name*', 'placeholder', 'woocommerce'),
            'required' => true,
           'class'    => array( 'form-row-first' ),
        );
        $fields['billing']['billing_last_name'] = array(
            'label' => '',
            'placeholder' => _x('last Name*', 'placeholder', 'woocommerce'),
            'required' => true,
           'class'    => array( 'form-row-last' ),
        );
        $fields['billing']['billing_company'] = array(
            'label' => '',
            'placeholder' => _x('Company Name', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('checkout-billing-company')
        );
        $fields['billing']['billing_address_1'] = array(
            'label' => '',
            'placeholder' => _x('Address(Line 1)*', 'placeholder', 'woocommerce'),
            'required' => true,
            'class' => array('checkout-billing-addressL1')
        );
         $fields['billing']['billing_address_2'] = array(
            'label' => '',
            'placeholder' => _x('Address(Line 2)*', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('checkout-billing-addressL2')
        );
         $fields['billing']['billing_email'] = array(
            'label' => '',
            'placeholder' => _x('Email Address*', 'placeholder', 'woocommerce'),
            'required' => true,
            'class' => array('form-row-first')
        );
        $fields['billing']['billing_phone'] = array(
            'label' => '',
            'placeholder' => _x('Phone Number', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('form-row-last')
        );
        $fields['billing']['billing_city'] = array(
            'label' => '',
            'placeholder' => _x('Town/City', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('form-row-first')
        );

$fields['billing']['billing_state'] = array(
            'label' => '',
            'placeholder' => _x('State/County', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('form-row-first')
        );
    $fields['billing']['billing_postcode'] = array(
            'label' => '',
            'placeholder' => _x('Zip/Postcode', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('form-row-first')
        );
        $fields['billing']['billing_country'] = array(
            'label' => '',
            'type' => 'select',
            'placeholder' => _x('Country', 'placeholder', 'woocommerce'),
            'required' => false,
            'class' => array('form-row-last'),
              'options'    => $countries
        );
        return $fields;
    }

add_filter('woocommerce_checkout_fields', 'add_wc_custom_fields');