Try this:
Move class-main-header.php into your child theme so:
customizr
…
customizr-child
–parts (create with New Folder)
class-main-header.php
Line 125 (before):
<h1><a class="site-logo" href="<?php echo esc_url( home_url( '/' ) ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name' , 'display' ) ); ?> | <?php bloginfo( 'description' ); ?>"><img src="<?php echo $logo_src ?>" alt="<?php _e( 'Back Home' , 'customizr' ); ?>" <?php echo $logo_img_style ?>/></a>
Line 125 (after)
<h1><a class="site-logo" href="https://mysite.com" target="_blank" title="<?php echo esc_attr( get_bloginfo( 'name' , 'display' ) ); ?> | <?php bloginfo( 'description' ); ?>"><img src="<?php echo $logo_src ?>" alt="<?php _e( 'Back Home' , 'customizr' ); ?>" <?php echo $logo_img_style ?>/></a>
(Think is very close to what you need!)