Gimana cara nyatuin data di Laravel?

Halo gan, saya mau tanya, cara nyatuin data group_code ke sub_group_code gmn ya? jadi ketika kita milih group_code yg dipilih nanti hasilnya nyatu di field sub_group_code

group_code

https://ibb.co/bb5SGNY

sub_group_code

https://ibb.co/31hpvsT

Tampilan Program

/coa (group_code)

https://ibb.co/F6ZzT4c

Tampilan input data /coasub (sub_group_code). nah jadi ketika kita ngambil data dari group_code hasilnya nyatu ke sub-group code

https://ibb.co/B66ghXp

/coasub (buat nyatuin group_code ke dalam sub_group_code)

jadi tampilan /coasub ini harusnya di sub-Group Code hasilnya 10.20 bukan kepisah group_code 10, sub-group code 20. gt gan.

https://ibb.co/kGzFBRd

source code /coasub (sub_group_code) ADD.BLADE.PHP

<div class="modal-body">
                <form action="/coasub/insert" method="post">
                    {{ csrf_field() }}
                <div class="form-group">
                    <label>Group Code</label>
                <select class="custom-select d-block w-100" id="group_id" name="group_id" required>
                    <option value="">Pilih Group Code...</option>
                    @foreach($coa_group as $li)
                    <option value="{{($li->group_code)}}">{{$li->group_code}}</option>
                    @endforeach
                </div>
                </select>
                <div class="form-group">
                    <label>Sub Group Code</label>
                    <input name="sub_group_code" input type="text" id="sub_group_code" class="form-control" placeholder="Sub Group Code .." required>
                </div>
                <div class="form-group">
                    <label>Description</label>
                    <input name="description" input type="text" id="description" class="form-control" placeholder="Description .." required>
                </div>
            </div>

InsertController

    public function coasubinsert(Request $request)
    {
        // insert data ke table coasub
        $this->validate($request,[
        'group_id' => 'required',
        'sub_group_code' => 'required',
        'description' => 'required'
        ]);

        Coasub::create([
        'group_id' => $request->group_id,
        'sub_group_code' => $request->sub_group_code,
        'description' => $request->description
        ]);
        session()->flash('status', 'Data Berhasil di Tambahkan');
        // alihkan halaman ke halaman coasub
        return redirect('/coasub');
    }

Jika ada yg kurang jelas, bisa ditanyakan gan