8 – To edit a Web Form value so that the column name in a table in the UI may be any

I have an submission form that shows all form submissions in a custom column table that I assemble from my form elements that I've created. I also use a built-in Drupal column named & # 39; complete & # 39; that shows the date and time of the submissions. I have to change this column name to "sent at".

I tried theme_table and module_table Methods to edit the value, but I can not make these methods. When I tried hook_form_alter I can not see the table values ​​if I edited them with var_dump ($ form)[] Array. I kept the command (_context) in the twig file of the table, and I am able to see the values ​​of the table, and the value comes from _context-> few layers Drupal Core Template AttributeString.

How do I use this information in form_alter or another hook to handle this string value?

I do not know how to use the _context array in the form_alter method. when I tried it[‘_context’] it gives me zero.