How dynamically change subcateory?

But my point of view all category which show and click any category after open related to subcategory.. This is my view file of model code

<!-- Button to Open the Modal -->

  <div class="form-group col-md-8">
  <button type="button" class="form-control" data-toggle="modal" data-target="#myModal">
Category  </button>

  <!-- The Modal -->
  <div class="modal" id="myModal">
<div class="modal-dialog modal-lg" >
      <div class="modal-content">

        <!-- Modal Header -->
        <div class="modal-header">
          <h4 class="modal-title">Category</h4>
          <button type="button" class="close" data-dismiss="modal">&times;</button>
        </div>

        <!-- Modal body -->
        <div class="modal-body">
                <div class="row">
                    <div class="col-md-4" >
                                <a href="#" name="category" id="category" >            
                                    @foreach($categories as $category)
                                    <option value=""></option>
                                    @endforeach
                                 </a>

                    </div>
                      <div class="col-md-4 ">
                        <a href="#" name="subcategory" id="subcategory" >
                            @foreach($subcategories as $subcategory)
                            <option value=""></option>
                            @endforeach
                         </a>

                      </div>
                      <div class="col-md-4">
                        hhh
                      </div>
              </div>
        </div>
      </div>
    </div>
  </div>

</div>

This is my controller

public function create()
{
    $categories = Category::all();
    $subcategories = Subcategory::all();

    return view('post.create', compact('categories', 'subcategories'));
}

This is route:

Route::get('/post/create', 'PostController@create')->name('post.create');

I created api but don't know how to use. This is my API

public function getSubcategory(Request $request)
{
    $id = $request->id;
    $subcategories = Subcategory::where('category_id',$id)
                         ->select('subcategory','id')
                         ->pluck('subcategory', 'id');
    

    return json_encode($subcategories);
}

API route

Route::get('api/getSubcategory/{id}', 'PostController@getSubcategory');

How can I do this runtime in model change subcategory related to category please help me

I am newbie in this...

via Chebli Mohamed