not working

Dear Sir,
I beginner for the word press
I tried to added this code part for function.php but its not working

wheres to add this code part?

List of fields to modify (based on wc checkout):
['billing']['billing_first_name']
['billing']['billing_last_name']
['billing']['billing_company']
['billing']['billing_address_1']
['billing']['billing_address_2']
['billing']['billing_city']
['billing']['billing_postcode']
['billing']['billing_country']
['billing']['billing_state']
['billing']['billing_email']
['billing']['billing_phone']
['order']['order_comments']
Modifying or removing existing fields
// Hook in to form
add_filter( 'boopis_rfq_form_fields' , 'custom_override_rfq_fields' );

// Our hooked in function - $fields is passed via the filter!
function custom_override_rfq_fields( $fields ) {

    // Remove billing first and last name
    unset($fields['billing']['billing_first_name']);
    unset($fields['billing']['billing_last_name']);

    // Make phone number optional
    $fields['billing']['billing_phone']['required'] = false;

    // Modify name and class of postcode 
    $fields['billing']['billing_postcode'] = array(
        'label'     => __('Zip Code', 'woocommerce'),
        'placeholder'   => _x('Zip Code', 'placeholder', 'woocommerce'),
        'required'  => false,
        'class'     => array('form-row-wide'),
        'clear'     => true
    );

  return $fields;
}
Adding new custom fields
Add the new field
// Add new custom field
add_action( 'boopis_rfq_after_order_notes', 'custom_select_referal_rfq' );

function custom_select_referal_rfq( $rfq ) {

    woocommerce_form_field( 'referal', array(
        'type'          => 'select',
        'class'         => array('form-row-wide'),
        'label'         => __('How did you hear about us?'),
        'required'          => true,
        'clear'         => false,
        'options'       => array(
            ''                      => __('Select Option', 'boopis-woocommerce-rfq' ),
            'friend'            => __('Friend', 'boopis-woocommerce-rfq' ),
            'coworker'      => __('Coworker', 'boopis-woocommerce-rfq' )
        ),
    ), $rfq->get_value( 'referal' ));

}
Validate the new field
// Validate new custom field
add_action('boopis_rfq_process', 'custom_select_referal_rfq_process');

function custom_select_referal_rfq_process() {
  // Check if set, if its not set add an error.
    if ( empty($_POST['referal']) ) {
        wc_add_notice( __( 'You must select the referal field.' ), 'error' );
    }
}
Update the new field
// Update new custom field
add_action( 'boopis_rfq_update_order_meta', 'custom_select_referal_update_order_meta' );

function custom_select_referal_update_order_meta( $order_id ) {
    if ( ! empty( $_POST['referal'] ) ) {
        update_post_meta( $order_id, 'Referal', sanitize_text_field( $_POST['referal'] ) );
    }
}
See WooCommerce Docs for more details.

Change redirect url
Add the shortcode [boopis_rfq] to your tahnk you page “My Page Name”

// Change redirect url
add_filter( 'boopis_rfq_redirect_url', 'my_custom_redirect_url' );

function my_custom_redirect_url() {
    $page = get_page_by_title( 'My Page Name' );
    return get_permalink( $page->ID );
}

please help me to fix this issue
thanks