app.module.ts

import { BrowserModule } from '@angular/platform-browser';
...
import { ChatComponent } from './chat/chat.component';

@NgModule({
  declarations: [
    ...
    ChatComponent,
  ],
  imports: [
   ...
    RouterModule.forRoot([
      { path: '', component: ChatComponent },
      { path: 'join', component: JoinComponent },
    ]),
  ],
  providers: [],
  bootstrap: [AppComponent],
})
export class AppModule {}