How alter submit user_pass_reset?
From \Drupal\user\Form\UserPasswordResetForm::buildForm:

&lt;?php
$form['#action'] = Url::fromRoute('user.reset.login', [
  'uid' =&gt; $user-&gt;id(),
  'timestamp' =&gt; $timestamp,
  'hash' =&gt; $hash,
])-&gt;toString();
?&gt;


If you look at the form in your browser, you can see that it directly POSTS to that other route. as a result of that, your submit isn't called because for that, it would need to actually submit to itself again.

That then points to \Drupal\user\Controller\UserController::resetPassLogin(), which calls user_login_finalize(), which calls user_login().

Depending on what you want to do on submit, you can either do in hook_user_login() or by altering that route.