How do I upload file on click only?

public $import_file = null;

    protected function getFormSchema(): array
    {
        return [
            Section::make('Import User Instructions')
                ->description('Instructions for importing users into the system')
                ->schema([
                    \Filament\Forms\Components\View::make('partials.import-instructions'),
                    FileUpload::make('import_file')
                        ->label('Import File')
                        ->acceptedFileTypes(['text/csv', 'application/vnd.ms-excel'])
                        ->helperText('Upload an Excel (.CSV) file with the required user data.'),
                ])
                ->compact()
                ->collapsible()
                ->footerActions([
                    Actions\Action::make('importUsers')
                    ->label('Import Users')
                        ->button()
                        ->color('success')
                        ->action(fn() => $this->importUsers()),
                ])
                ->footerActionsAlignment(Alignment::End),
        ];
    }

    public function importUsers(): void
    {
        $this->validate([
            'import_file' => 'required|file|max:2048',
        ], [
            'import_file.required' => 'Please upload a file.',
        ]);

        Import::start(
            file: $this->import_file
        );

        Notification::make()
            ->title('File Uploaded')
            ->success()
            ->send();
    }