How to edit a web form value so that the column name can be as required in a table in UI I have a submissions form where I am displaying all the form submissions in a table with custom columns, which I build from my form elements I created. But also I am using an built-in drupal column called 'completed', which will display the date and time of the submissions. I need to edit this column name to 'submitted at'.

I tried theme_table and module_table methods to edit the value but I am not able to hit those methods. When I tried hook_form_alter I am not able to see the table values when I did var_dump($form) to edit them in form[] array. I kept knit(_context) in the twig file of the table and I am able to see the values of the table and the value is coming from _context->few layers  Drupal\Core\Template\AttributeString.

How do I use this info in form_alter or any other hook to edit that string value? 

Like I don't know how to use _context array in form_alter method. when I tried form['_context'] its giving me null.
I was able to edit it using theme_preprocess_table method below is the method which I used.

   function theme_preprocess_table(&amp;$variables)
   {
       $variables['header']['completed']['content'] = 'your requirement';
   }