Relation manager in custom page

class EditAmenities extends Page implements Forms\Contracts\HasForms
{
    use Forms\Concerns\InteractsWithForms;

    protected static string $resource = ListingResource::class;

    protected static string $view = 'filament.resources.listing-resource.pages.edit-listing.edit-amenities';

    protected function getActions(): array
    {
        return [];
    }

    protected function getTitle(): string
    {
        return '';
    }
    public $amenities;
    public $listing;
    public Listing $record;

    public function mount(): void
    {
        $listing = $this->listing = Listing::findOrFail($this->record->id);
        $this->form->fill([
            'amenities' => $listing->amenities
        ]);
    }

    public function getFormModel(): Listing
    {
        return $this->listing;
    }

    public function update()
    {
        $this->listing->update($this->form->getState());

        Notification::make()
        ->title('Saved successfully')
        ->success()
        ->send();
    }