I hope These Method Help You :

$model = Model::find($request->model_id);
$nested = $model->nested_prop;
$nested['foo']['bar']['x'] = 2;
$model->nested_prop = $nested;
$model->save();

OR

$model = Model::find($request->model_id);
data_set($model->nested_prop, 'foo.bar.x', 2);
$model->save();