Hi Piyuesh
Here you have change the text that argument should be 1.
+ '#...

Hi Piyuesh

Here you have change the text that argument should be 1.
+ '#description' => $this->t('Add the argument of search keyword to fetch the results.e.g. example.com/result/keyword if keyword is a argument then enter 1.'),
+ ];

We are using
$path = \Drupal::request()->getPathInfo();
$args = explode('/', $path);
In above $args is an array.
Array
(
[0] =>
[1] => result
[2] => keyword
)

So keyword is the 2 argument. So we user has to enter 2.