[Parent/Child] How to Update parent_id field from Form?

[HC-CHAN]

I can reorder and move from one parent to another parent for an item from listing view, but having trouble to update parent_id for particular item from edit form.

Declaring a Select Field for parent in Controller.

public function getForm(TwillModelContract $model): Form
{
    
    $form = parent::getForm($model);
    $form->add(
        Select::make()->name('parent_id')->label('Parent Menu')
        ->options(
            Sitemenu::all()->mapWithKeys(function ($sitemenu) {
                return [$sitemenu->id => $sitemenu->title];
            })->prepend('None', '')->toArray()
        )
        
    );

And having a afterSave function In Repository.php.
we found that $fields['parent_id'] field alway return last saved value ONLY
If last saved was 5, it will always return 5, no matter what you chose from the Select Dropdown which named it as "parent_id"
Select::make()->name('parent_id')

public function afterSave($model, $fields): void
{
    if (isset($fields['parent_id'])) {
        $model->parent_id = $fields['parent_id'] ?: null; // Set null if empty
    }

    $model->save();
    parent::afterSave($model, $fields);
}

Not sure how can update Parent Level from Form, any idea?