How to send textarea formular to function in other file

[eluser]Unknown[/eluser]
Greetings.

I have to edit a finished project, which was written with php, html, codeigniter, ajax, javascript and json.

Problem is, I have only knowledge in php and html. I spent many hours to understand this project and codeigniter. The other three things are not that important.
Enough introducing:
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I want to pass a written text in a textarea formular to the function

Code:

changeStatus()

in an other file. After that, the passed text should be written in a database.

Here the formular:

Code:

<form method="POST" id="changeStatus" action="<?$this->model->changeStatus();?>">
    
&lt;textarea name="statustext"&gt;&lt;?=$showStatus['status_text'];?&gt;&lt;/textarea&gt; </br>

&lt;input type="submit" name="status_aendern" value="Änderung vornehmen"&gt;
&lt;/form&gt;

How can I write this, that the text will be passed to the function? Any ideas?

Thanks for your help!