How to delete unchecked checkboxes in laravel

I have displayed checkboxes of subjects in laravel.In which some checkboxes are already checked ,come from database.When any checkbox is checked the new subject is added in database. The actual problem is that there are other subjects checkboxes that are not saved in database. The issue to resolve is that,when user uncheck any checkbox of subject which is saved in database should be deleted from database

In blade

@foreach($grades as $grade) {{$grade->name}}

@foreach($grade->subject as $subject)
• {!!Form::checkbox('check_list[]',$grade->id.'-'.$subject->id,$yes,['class'=>''])!!} {{$subject->name}}
@endforeach

@endforeach

in Controller

if($request->check_list){ $user_id = auth()->user()->id; $i = 0; $j = 0;

                foreach ($request->check_list as $data) {
                    $array1[$i] = explode('-', $data);
                    $i++;
                }
                foreach ($array1 as $j => $data1) {

                    $hasSubject = UserSubject::where('user_id', $user_id)->where('subject_id', $data1[1])->where('grade_id', $data1[0])->first();

                    if(is_null($hasSubject)) {

                        $user_subjects = new UserSubject();
                        $user_subjects->user_id = $user_id;
                        $user_subjects->grade_id = $data1[0];
                        $user_subjects->subject_id = $data1[1];
                        $user_subjects->status = 1;
                        $user_subjects->created_at = date("Y-m-d H:i:s");
                        $user_subjects->updated_at = date("Y-m-d H:i:s");
                        // dd($user_subjects);
                        $user_subjects->save();

                        $j++;
                    }
                }