Hello Gary

Supposedly, your URL is https://yourwebsite.com/?value_x=123

The data pulled from the database creates a table using a query similar to this:

SELECT * FROM table WHERE value_x = %VAR1%

After that, you can use a hook for dynamic placeholders (place it in functions.php of your theme, or your child theme):

function updateVAR1($tableID){
  global $wdtVar1;
      //check is set GET parametar value_x
    if(isset($_GET['value_x'])){
        //get value from form field
        $wdtVar1 = $_GET['value_x'];
    }
  }
add_action('wpdatatables_before_get_table_metadata', 'updateVAR1');

I hope this helps.