How can I get the value of a field that is not in the relationship

protected function getFormSchema(): array
{
 return [   Forms\Components\Toggle::make('display_hp')
    ->reactive(),
        Forms\Components\Group::make()
  ->relationship('article')
  ->schema([                       TextInput::make('hp')
         ->visible(fn($get): bool => $get('display_hp')),
  )]
];
}