Work with the function add_rewrite_rule()

Hello!

I’m trying to understand the function add_rewrite_rule()
Now a link to the first post looks as: https://localhost/?p=1
In the setting of WordPress permalinks by default “https://localhost/?p=123”

Create a new rule for the first post in functions.php

Code:

function NewRuleForFirstPost ()
{
    add_rewrite_rule('first_post/?$', 'index.php/?p=1', 'top');
    flush_rewrite_rules();
}
add_action('init', 'NewRuleForFirstPost');

But this method does not work – in the address line shows the /?p=1 ??
help me, pls!

P.S. sorry for bad english!