how to save multiple objects to database with passport-local-mongoose?

I want to register users to my mongoDB database using passport-local-mongoose node package, and I have no problem with that, but what I want is to add more than the username and password to the database: for example ( their first and last names, their roles and pretty much anything neccesssary for the user)

how can I do that with passport-local-mongoose, or is there any other way than with that package, I already tried to add the other objects to the database but for some reason it didn't work. here's what I tried to get the extra objects to the database:

app.post('/register', function(req, res){
    User.register({username: req.body.username}, req.body.password, function(err, user) {
        if (err) { 
            console.log(err);
            res.redirect('/register')
         } else{
            passport.authenticate('local')(req, res, function(){
                User.updateOne({ username: req.body.username }, { $set: { firstName: 'firstnName', lastName: 'lastName' } })
                res.redirect('/secrets')
            })
           };
      });
})

and as you can see I used mongoose's updateOne function to set the new values manually but for some reason I don't see them in the database. and also I have contained the first and last names in the User model schema here's the schema:

const userSchema = new mongoose.Schema ({
    email: String,
    password: String,
    firstName: String,
    lastName: String
})

any suggestions?

I found the answer, you have to specify the other values of the schema with the username field object:

app.post('/register', function(req, res){
    User.register({username: req.body.username, firstName: req.body.firstName, lastName: 
        req.body.lastName}, req.body.password, function(err, user) {
        if (err) { 
            console.log(err);
            res.redirect('/register')
         } else{
            passport.authenticate('local')(req, res, function(){
                res.redirect('/secrets')
           };
      });
})

you should change the schema to this:

const userSchema = new mongoose.Schema ({
    username: String,
    password: String,
    firstName: String,
    lastName: String
})