What is EntityManager

Using EntityManager you can manage (insert, update, delete, load, etc.) any entity. EntityManager is just like a collection of all entity repositories in a single place.
You can access the entity manager via DataSource. Example how to use it:
import { DataSource } from "typeorm"
import { User } from "./entity/User"
const myDataSource = new DataSource(/*...*/)
const user = await myDataSource.manager.findOneBy(User, {
id: 1,
}) = "Umed"