Works on secondary site in BP-multi-network?

Hey Ron, fantastic plugin- just what the doctor ordered!

I want to know how to force all BP pages to a secondary site/subdomain within each BP network?? like in:
https://wpmututorials.com/news/new-features/multiple-buddypress-social-networks/#comment-12145

I know I have to define the desired $site_id for each network_id in a mu-plugin,
but unfortunately I’m no PHP programmer!

So, what is missing here?

<?php
/* Set which site ID BuddyPress will run on in each network:  
https://codex.buddypress.org/getting-started/customizing/changing-internal-configuration-settings/ 
https://make.www.ads-software.com/core/tag/4-6+dev-notes/page/2/
*/

function pl_bp_network_site_filter
      global $wpdb;
	
    	if ( $wpdb->siteid = 1 || define ( 'BP_ROOT_BLOG', $site_id ) );
	// Define this function for sharing BP throughout/across the sites of this network
	//define ( ‘BP_ENABLE_MULTIBLOG’, true );
	
	if ( $wpdb->siteid = 2 || define ( 'BP_ROOT_BLOG', $site_id );
	// Define this function for sharing BP throughout/across the sites of this network
	//define ( ‘BP_ENABLE_MULTIBLOG’, true );
	
	if ( $wpdb->siteid = 3 || define ( 'BP_ROOT_BLOG', $site_id );
        // Define this function for sharing BP throughout/across the sites of this network
	//define ( ‘BP_ENABLE_MULTIBLOG’, true );

add_filter( 'bp_get_root_site_id', 'filter_root_site_id' ); // return site ID integer

	}
}

/**
 * Call when the plugin is activated
 */
register_activation_hook(__FILE__, 'define-BP-root');

Thanks for your time!

https://www.ads-software.com/plugins/bp-multi-network/