CODE EXAMPLE FOR PHP

extend woocommerce user fields edit-account

// Add the custom field "favorite_color"
add_action( 'woocommerce_edit_account_form', 'add_favorite_color_to_edit_account_form' );
function add_favorite_color_to_edit_account_form() {
    $user = wp_get_current_user();
    ?>
        <p class="woocommerce-form-row woocommerce-form-row--wide form-row form-row-wide">
        <label for="favorite_color"><?php _e( 'Favorite color', 'woocommerce' ); ?></label>
        <input type="text" class="woocommerce-Input woocommerce-Input--text input-text" name="favorite_color" id="favorite_color" value="<?php echo esc_attr( $user->favorite_color ); ?>" />
    </p>
    <?php
}

// Save the custom field 'favorite_color' 
add_action( 'woocommerce_save_account_details', 'save_favorite_color_account_details', 12, 1 );
function save_favorite_color_account_details( $user_id ) {
    // For Favorite color
    if( isset( $_POST['favorite_color'] ) )
        update_user_meta( $user_id, 'favorite_color', sanitize_text_field( $_POST['favorite_color'] ) );

    // For Billing email (added related to your comment)
    if( isset( $_POST['account_email'] ) )
        update_user_meta( $user_id, 'billing_email', sanitize_text_field( $_POST['account_email'] ) );
}