Using the child theme functions.php to change the customizer.php on parent theme

Put this code in function.php. create custom section in customizer for logo :

<?php
add_action('customize_register', 'theme_footer_customizer');
function theme_footer_customizer($wp_customize){
    //adding section in wordpress customizer   
    $wp_customize->add_section('footer_settings_section', array(
      'title'          => 'Footer Text Section'
    ));
    //adding setting for footer logo
    $wp_customize->add_setting('footer_logo');
    $wp_customize->add_control(new WP_Customize_Upload_Control($wp_customize,'footer_logo',array(
     'label'      => 'Footer Logo',
     'section'    => 'footer_settings_section',
     'settings'   => 'footer_logo',
     ))); 
}