Insert data into a table and update another table from one form

I have 3 tables purchase, purchase_details and product. When purchase details added with product information only qty will be added in product table and it will be sum with the existing product qty.

I tried

COntroller:

if($request->has('publish')){
        $purchase = new Purchase();
        $purchase['stockID'] = $request->stockID;
        $purchase['supplier_id'] = $request->supplyer_id;
        $purchase['payment_status_id'] = $request->payment_status;
        $purchase['purchase_date'] = $request->purchase_date;
        $purchase['draft'] = 1;
        $user_id = Auth::user()->id;
        $purchase['created_by_id'] =$user_id;
        // dd($purchase);
        $purchase->save();
        $purchase_id = $purchase->id;
        $insert_details_array=array();
        // dd($income_id);
        foreach($request->addmore as $details){
            // $data = new incomes_details();
            $data['purchase_id'] = $purchase_id;
            $data['product_id'] = $details['product_id'];
            $data['purchase_qty'] = $details['quantity'];
            $data['purchaseprice'] = $details['purchaseprice'];
            $totalpurchase = $data['purchaseprice']*$data['purchase_qty'];
            $getqty = $data['purchase_qty'];
            $data['total_amount'] = $totalpurchase;
            $data['created_at'] = now();
            $insert_details_array[]=$data;
            unset($data);
            // $data->save();
            // dd($data);
        }
        // dd($getqty);
        // dd($insert_details_array);
        
        return redirect()->back();
    }

purchase Model:

protected $fillable = ['stockID','supplier_id','payment_status_id','purchase_date','created_by_id'];

Purchase Details Model: protected $fillable = ['purchase_id','product_id','purchase_qty'];

How can i update product qty in product table.

please help.

suggest me.