Once you have defined a filter, you are ready to attach it to a resource. Each resource generated by Nova contains a filters method. To attach a filter to a resource, you should simply add it to the array of filters returned by this method: 
use Laravel\Nova\Http\Requests\NovaRequest;

// ...

/**
 * Get the filters available for the resource.
 *
 * @return array<int, \Laravel\Nova\Filters\Filter>
 */
public function filters(NovaRequest $request): array
{
    return [
        new Filters\UserType,
    ];
}

​
Searchable Select Filters

Select filters may be optionally searchable. To allow your select filter to be searchable, invoke the searchable method when registering your filter:
app/Nova/~Resource.php
use Laravel\Nova\Http\Requests\NovaRequest;

// ...

/**
 * Get the filters available for the resource.
 *
 * @return array<int, \Laravel\Nova\Filters\Filter>
 */
public function filters(NovaRequest $request): array
{
    return [
        Filters\UserType::make()
            ->searchable(),
    ];
}