how to make changes in an array and keep them in typescript?

I'm making a website with angular, for this I need a login and a page to register new users, I'm using a service to save users, in this service I have an arrangement with users, the problem is that when I add a new user through the page and then I go to the login, the new user added does not work, that is as if I had never registered it.

here the service code:

import { Injectable } from '@angular/core';
import { usuario } from './app.component';

@Injectable({
  providedIn: 'root'
 })
 export class UserListService {

 constructor() { 

 }

 //cuenta del administrador
 admin = new usuario("admin","[email protected]","admin");

 // arreglo donde se guardan los usuarios
 usuarios = [this.admin];

 //metodo para agregar usuarios nuevos
 agregar(usuario){
    this.usuarios.splice(1,0,usuario);
 }

}

here the code of the registry:

import { Component, OnInit } from '@angular/core';
import { usuario } from '../app.component';
import { UserListService } from '../user-list.service'

@Component({
  selector: 'app-registrar',
  templateUrl: './registrar.component.html',
  styleUrls: ['./registrar.component.css']
})
export class RegistrarComponent implements OnInit {

  constructor(
     public user:UserListService
   ) { }


  nuevo;

  ngOnInit() {
  }

  //metodo para registrar un usuario nuevo
  registrar(id,email,password,password2){
      if(password == password2){  
         this.nuevo = new usuario(id,email,password);
         this.user.agregar(this.nuevo);
      }
  }

}

here the login code:

import { Component, OnInit } from '@angular/core';
import {Router} from '@angular/router';
import { usuario } from '../app.component';
import { UserListService } from '../user-list.service'

@Component({
  selector: 'app-iniciar-sesion',
  templateUrl: './iniciar-sesion.component.html',
  styleUrls: ['./iniciar-sesion.component.css']
})
export class IniciarSesionComponent implements OnInit {

    constructor(private router:Router,
    public user: UserListService) { 
    }


    ngOnInit() {
    }

    // arreglo que guarda los usuarios registrados 

    usuarios = this.user.usuarios;

    // metodo para el inicio de sesion
    redireccion(contra,email){
    // se comprueba que si se hallan insertado el email y la contraseña
       if(contra != null && contra != "" && email!= null && email != ""){
           for(let i of this.usuarios){
           // se mira que el usuario ingresado si sea el correcto
              if(email == i.email && contra == i.password){
                this.router.navigate(["ver"]); 
              }
           }
       }
    }
}