Add secondary logo for for a specific pages.

functions.php

<?php

/** Add secondary logo for for a specific pages. */
add_filter( 'get_custom_logo', 'custom_secondary_logo_callback' );
/**
 * @link https://codex.wordpress.org/Conditional_Tags
 */
function custom_secondary_logo_callback( $logo ){
	$your_custom_logo = "Your Custom Logo";// Add your custom logo maerkup instead.
	// is_singular() find more conditional tags from here -- https://codex.wordpress.org/Conditional_Tags
	if ( is_singular() ) {
		$logo = $your_custom_logo;
	}
	return $logo;
}