Want to disable or remove the item that's selected in the above dropdown from the multi select below

Ember CLI
1

Hi everybody - I have a question in Ember, I have a dropdown when an Item selected in the dropdown - it should either remove item or disable item from the multi-select below, how can I do that, my controls are set in the below way - any suggestion please - thank you.

                <div class="row">
                    <div class="form-group">
                        <label for="section" class="col-md-4 control-label">Assigned Investigator</label>
                        <div class="col-md-6">
                            <select class="form-control" id="assignedInspectorSelect" required="required">
                                <option value="">Select...</option>
                                {{#each  model.staffonly as |inspector|}}
                                {{#if (is-same model.imscase.inspectorId inspector.id)}}
                                <option value="{{inspector.id}}" selected>{{inspector.name}}</option>
                                {{else}}
                                <option value="{{inspector.id}}">{{inspector.name}}</option>
                                {{/if}}
                                {{/each}}
                            </select>
                        </div>
                    </div>
                    <div class="col-md-12">
                        <div class="form-group">
                            <label for="section" class="control-label">Owner(s)</label>
                            {{#multiple-select
                                multiple="multiple"
                                list=model.investigators
                                select=model.imscase.assignedToInvestigators
                                selector='id'
                                required=true
                                id='assignedToInvestigators' as |item id|}} 
                                {{multiple-select-option value=item.id content=item.name}}
                            {{/multiple-select}}
                        </div>
                    </div>
                </div>