在app.module.ts中引入Firestore模块并将它添加到providers数组中。

示例代码：

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';

// Import the Firestore module
import { AngularFireModule } from '@angular/fire';
import { AngularFirestoreModule } from '@angular/fire/firestore';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    // Add both the Firebase and Firestore modules to imports
    AngularFireModule.initializeApp(environment.firebase),
    AngularFirestoreModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }