Don’t record activity by the site admins

Hi I am using the Elbee Elgee theme and I don’t want the site to show admin activity. I found this code and it was said to add it to the bp-custom.php but I don’t know a page with this name.

// Don’t record activity by the site admins or show them as recently active
function my_admin_stealth_mode(){
if ( is_site_admin() ) {
global $bp;
remove_action(‘wp_head’,’bp_core_record_activity’);
delete_user_meta($bp->loggedin_user->id, ‘last_activity’);
}

thanks