how to add form action twig template form
I am assuming you are building this form with Form API and not plain HTML (don't do that). You need to add the attributes to ensure you get everything you need.

&lt;form{{ attributes }}&gt;


See the main form.html.twig template: https://api.drupal.org/api/drupal/core%21modules%21system%21templates%21form.html.twig/8.4.x

In general, I advise you to theme the form elements themselves instead of stitch the form together like this, because you will likely be missing the things in the form Drupal adds behind the scenes to a rendered form.