TypeError: app.currentUser.mongoClient is not a function

const appId = 'myAppId';
        const appConfig = {
          id: appId,
          timeout: 100000,
        };
const app = new Realm.App(appConfig);
const mongodb = app.currentUser.mongoClient("mongodb-atlas");

when i’m using above code in react native getting error “TypeError: app.currentUser.mongoClient is not a function”

Same Issue:
on going through dov i found “To access a collection, create MongoDB service handle for the user that you wish to access the collection with:”

there is some meaning in "MongoDB service handle for the users, which i am unable to understand.

HELP