How to create a custom_where() method by extending CodeIgniter's query builder

How can I properly make my own implementation of a query builder method in CodeIgniter.

$this-db
    ->from('myTable')
    ->where('id', 1)
    ->custom_where('name', 'customsValues')
    ->get()

There values are irrelevent here. I've already built a class that extends en current CI_DB_query_builder, but I have no idea where to set my class to be used as the primary query builder.

I've found the answer to my question. However, any other good answer is welcome since mine is not the prettiest.

First let me walk you through what I was trying to do.
I wanted to use Tightenco's collect library to use collection rather than array. This way I could use more intuitive chain array function:
$this->db->from('...')->results()->map(function($items) { ... })->toArray();

Then, i wanted to have my own function, such as where_if.

I started by making my own query builder class that extended from CI_DB_query_builder. I have an example below:

<?php
require BASEPATH . 'database/DB_query_builder.php';


class CustomQueryBuilder extends CI_DB_query_builder {
    public function where_if($where, $value, $condition) : CustomQueryBuilder {
        if($condition) {
            $this->where($where, $value);
        }
        return $this;
    }

    public function results() : \Tightenco\Collect\Support\Collection {
        return \Tightenco\Collect\Support\Collection::make($this->get()->result_array());
    }
}

To link this class as the main Querybuilder, I had to change it in the file system/database/DB.php.
I changed the path of the require_once in line 171 :

require_once(APPPATH.'libraries/QueryBuilder/CustomQueryBuilder.php');

I also changed the alias class on line 182

class CI_DB extends CustomQueryBuilder { }

Please note that this is on codeigniter v3.0.6, your line number may differ.

Now, i needed to import some function so the autocomplete on PHPStorm would still point to my custom querybuilder, because once i used the function from, it returned a CI_DB_query_builder object.
Here is how I imported the function I used the most.

/**
 * Nothing changed here, for autocompletion only
 * @param mixed $from
 * @return $this|CI_DB_query_builder
 */
public function from($from) {
    parent::from($from);
    return $this;
}

I really hope this helps people that are trying the same thing. If you got any feedback on this project, please let me know !