title: How to manually reset Formik field to null (REACT)
body: <p>I need to reset value of this <code>Field</code> manually, for example on some click event which exists already I would like to set value of <code>assignedProductId</code> to null!</p>
  
  <p>Here is field:</p>
  
  <pre><code>  &lt;Field
          name="assignedProductId"
          component={Dropdown}
          options={this.state.Products}
          loading={this.state.isLoading}
          onChange={this.onProductChange}
       /&gt;
  </code></pre>
  
  <p>I have no idea how could I access this field and reset it's value manually...
  I red about <code>setFieldValue</code>, but I'm not sure how to access this Field so I might set it's new value..</p>
  
  <p>Thanks guys</p>
  
  <p>Cheers</p>