How update Value in configuration table form front office

[pippo67]

Hello,
I created a small form front office with an input field and a button.
I'm trying to update the value my friend in the configuration table with the value entered in my input field. I tried these instructions, but the value is not updated. Where am I doing wrong?

 

This is the coide of the myfirstmodule.php file  that should update the text my friend

public function changeValue( {

              $result = isset($_POST['text'])  ?  $_POST '[text']  :  ””;

              Configuration::updateValue('MYMODULE_NAME',  $result);

           }

 Thank you!