The easiest way is to use onclick= and then the name_of_function ();

for example:

 <div class="form-group RunningSQLScripts">
    <label for="inputStatus">Running My Scripts</label>
        <select id="inputStatus" name="RunningSQLScripts" class="form-control">
        <option selected disabled>--</option>
        <option onclick="RunScript1()">Delete Whole Table</option>
        <option onclick="RunScript2()">Run Script 3</option>
                                    
        </select>
 </div>

And then according to the function's name. Create the appropriate functions to run on click.

You can submit the form to the server and execute the request you need.

<?php
  $db = new mysqli('localhost', 'db_user', '1234', 'db_name');
  if($db->connect_errno)die('Error: '.$db->connect_error);
?>

<form name="runSQL" method="get">
    <div class="form-group RunningSQLScripts">
        <label for="inputStatus">Running My Scripts</label>
            <select id="inputStatus" name="RunningSQLScripts" class="form-control">
            <option selected disabled>--</option>
            <option value="RunScript1">Delete Whole Table</option>
            <option value="RunScript2">Run Script 3</option>                   
            </select>
            <input type="submit" value="Run">
     </div>
</form>

<?php
    $runSQL = $_GET['RunningSQLScripts'];
    
    switch($runSQL){
        case 'RunScript1':
            $db->query("truncate table `name`");
            echo '* Successfully deleted *';
        break;
        
        case 'RunScript2':
            $db->query("SQL");
            echo '* Successfully run *';
        break;
    }
?>

Easiest way to do it: fully working, Just add onchange='this.form.submit();'

<form id="companyForm" name="companyForm" class="form-horizontal" type=get>


<div class="form-group RunningSQLScripts">
    <label for="inputStatus">Running My Scripts</label>
    <select id="inputStatus" name="RunningSQLScripts" onchange='this.form.submit();' class="form-control">
        <option selected disabled>--</option>
        <option value="RunScript1">Delete Whole Table</option>
        <option value="RunScript2">Run Script 3</option>
                                    
        </select>
 </div>

</form>


<?php
$RunningSQLScripts = $_GET['RunningSQLScripts'];

$con = mysqli_connect('host','username','password','db');
if (!$con) {
    die('Could not connect: ' . mysqli_error($con));
}

mysqli_select_db($con,"db");

if ($RunningSQLScripts == "RunScript1") 
{

$sql="truncate TABLE `table_name1`;";  // truncate table table_name1
$result = mysqli_query($con,$sql);

}

mysqli_close($con);
?>