How to use the @nebular/theme.NbDatepickerModule.forRoot function in @nebular/theme

NbActionsModule,
    NbSearchModule,
    NbIconModule,
    NbMenuModule.forRoot(),
    NbTooltipModule,
    NbCardModule,
    NbInputModule,
    NbCheckboxModule,
    NbSelectModule,
    NbDialogModule.forRoot(),
    NgxMaskModule.forRoot(),
    NbToastrModule.forRoot(),
    ReactiveFormsModule,
    NbAlertModule,
    FormlyModule.forRoot(),
    NbDatepickerModule.forRoot(),
    FormlyBootstrapModule,
    Ng2FittextModule,
    NgBootstrapFormValidationModule.forRoot(),
  ],
  providers: [
    ElectronService, 
    NbMenuService, 
    NbDialogService, 
    AccountsService, 
    NbDatepickerDirective,
    {
      provide: ErrorHandler, 
      useFactory: errorHandlerFactory
    },
  ],
  entryComponents: [ConfirmDeleteComponent, AddEditWidgetModalComponent, AddEditFilterModalComponent, ColumnReferanceDialogComponent],

import { DatepickerFormsComponent } from './datepicker-forms.component';
import { DatepickerShowcaseComponent } from './datepicker-showcase.component';
import { DatepickerValidationComponent } from './datepicker-validation.component';
import { RangepickerShowcaseComponent } from './rangepicker-showcase.component';

@NgModule({
  declarations: [
    DatepickerFormsComponent,
    DatepickerShowcaseComponent,
    DatepickerValidationComponent,
    RangepickerShowcaseComponent,
  ],
  imports: [
    FormsModule,
    ReactiveFormsModule,
    NbDatepickerModule.forRoot(),
    NbInputModule,
    DatepickerRoutingModule,
  ],
})
export class DatepickerModule {}

import { DatepickerFormsComponent } from './datepicker-forms.component';
import { DatepickerShowcaseComponent } from './datepicker-showcase.component';
import { DatepickerValidationComponent } from './datepicker-validation.component';
import { RangepickerShowcaseComponent } from './rangepicker-showcase.component';

@NgModule({
  declarations: [
    DatepickerFormsComponent,
    DatepickerShowcaseComponent,
    DatepickerValidationComponent,
    RangepickerShowcaseComponent,
  ],
  imports: [
    FormsModule,
    ReactiveFormsModule,
    NbDatepickerModule.forRoot(),
    NbInputModule,
    DatepickerRoutingModule,
    NbCardModule,
  ],
})
export class DatepickerModule {}

NbWindowModule,
} from '@nebular/theme';

@NgModule({
  declarations: [AppComponent],
  imports: [
    BrowserModule,
    BrowserAnimationsModule,
    HttpClientModule,
    AppRoutingModule,

    ThemeModule.forRoot(),

    NbSidebarModule.forRoot(),
    NbMenuModule.forRoot(),
    NbDatepickerModule.forRoot(),
    NbDialogModule.forRoot(),
    NbWindowModule.forRoot(),
    NbToastrModule.forRoot(),
    NbChatModule.forRoot({
      messageGoogleMapKey: 'AIzaSyA_wNuCzia92MAmdLRzmqitRGvCF7wCZPY',
    }),
    CoreModule.forRoot(),
  ],
  bootstrap: [AppComponent],
  providers: [
    { provide: APP_BASE_HREF, useValue: '/' },
  ],
})
export class AppModule {
}

import { DatepickerFormsComponent } from './datepicker-forms.component';
import { DatepickerShowcaseComponent } from './datepicker-showcase.component';
import { DatepickerValidationComponent } from './datepicker-validation.component';
import { RangepickerShowcaseComponent } from './rangepicker-showcase.component';

@NgModule({
  declarations: [
    DatepickerFormsComponent,
    DatepickerShowcaseComponent,
    DatepickerValidationComponent,
    RangepickerShowcaseComponent,
  ],
  imports: [
    FormsModule,
    ReactiveFormsModule,
    NbDatepickerModule.forRoot(),
    NbInputModule,
    DatepickerRoutingModule,
    NbCardModule,
  ],
})
export class DatepickerModule {}