Defining a custom key name to selected colummns from results returned in Eloquent

I have an Eloquent scope search query like this that takes in input parameters like this:

"ECEC 301 Advanced Programming for Engineers Lab",
"ECEC 301 Advanced Programming for Engineers Lecture",
"ECEC 302 Digital Systems Projects Lab",
"ECEC 471 Introduction to VLSI Design Lab"

Using this Model:

public function scopeSearchWithType($query, $searchTerm) {
    return $query->where(
        DB::raw("subject_code || ' ' ||  course_no || ' ' || course_title || ' ' || instr_type"),
        'like',
        '%' . $searchTerm . '%'
    )->select(
        $searchTerm,
        'day',
        'time',
        'crn'
    );
}

As you can see, each input string is actually the combination of four different columns.

Anyways. When I run this query, this is the following result:

       "ECEC 471 Introduction to VLSI Design Lab": "ECEC 471 Introduction to VLSI Design Lab",
       day: "W",
       time: "09:00 am - 10:50 am",
       crn: "12506"
   }

As you can see, the key of $searchQuery is the name of the value. I would like to assign a custom name such as course_name to the key.

I've tried everything from class => $searchTerm to class as $searchTerm, but they did not work.