How to Change the Database Source from within an application - xampp

Question

I'm developing an app on xammp that allows you add multiple schools, and with each new school added, a new database is added. All that works fine.
The issue is in switching from database name to another database name in my db config. I have a form action "set_source" that triggers the setDBNAME action but get an uncaught error.
I tried the following code
class dbConfig
{
public $hostname = 'localhost'; //hostname for db connection
public $username = 'root'; // username for db connection
public $password = 'password'; //password for db conection
public $dbname = 'school1'; //this must be dynamically changeable
public $mysqli;
function setDBNAME($id)
{
$sql = "SELECT `school_name`, `subdomain`, `selected`, `url` FROM board.school WHERE school_id = $id AND selected = 'True'";
$data = $this->mysqli->execute_query($sql); //line triggering error
if($data) {
return new dbConfig(localhost, root, password, $data['url']);
}
else {
return null;
}
}
}
But Got the following error
Fatal error: Uncaught Error: Call to a member function execute_query()
on null in path\to\file\dbConfig.php:15 Stack trace: #0 path\to
\file\myaccountController.php(50): dbConfig->setDBNAME('1') #1
path\to\file\Controller11.php(29): myaccountController->set_source()
#2 path\to\file\myaccount.php(20): Controller11->run() #3 {main}
thrown in path\to\file\dbConfig.php on line 15
Any pointers and or solutions will be muchos gracias