Help Needed: Creating Functional Button

Hi, when I’m trying to give a function or action to a button, it doesn’t work as I thought. I’ve tried some ways but still didn’t work. Code of each trial I tried attached below.
Can anyone help me, please? Thanks in advance.

Here’s a snippet of my code:

Trial 1:

> <form method = "POST">
>        ... /* Form's body goes here */
>  <input type = "submit" name = "submit" value = "submit">
> </form>

And here’s the button test (in this case I used refresh page) but it results in error 405:

if (isset($_POST['submit'])){
        echo "<meta http-equiv='refresh' content='0'>";

And also, here’s my route.php

return [
‘routes’ => [
[‘name’ => ‘page#index’, ‘url’ => ‘/’, ‘verb’ => ‘GET’]

Trial 2:
<form action = "another.php" method = "POST">
This resulted in load the leftmost app in nextcloud (not the app)

Thanks in advance.