How to use installed mongodb on google cloud

I recently developed a react app with nodejs which depends on mongodb for its data. I have also just installed mongodb on Google Compute Engine and opened port 27017. However, my question is, how can i connect my application (I am using Mongoose) to the VM Instance.

Here is the connection string on localhost (my local machine), what should I change it to:

module.exports = {
    url: 'mongodb://localhost:27017/dapashirts'
}

Here is my server.js file:

const express = require('express');
const bodyParser = require('body-parser');
const cors = require("cors");

const app = express();

app.use(cors());
app.use(bodyParser.urlencoded({extended:true}));
app.use(bodyParser.json());

// Configuring the database
const dbConfig = require('./config/database.config.js');
const mongoose = require('mongoose');

mongoose.Promise = global.Promise;

// Connecting to the database
mongoose.connect(dbConfig.url, {
    useNewUrlParser: true, useUnifiedTopology: true, useCreateIndex: true
}).then(() => {
    console.log("Successfully connected to the database");    
}).catch(err => {
    console.log('Could not connect to the database. Exiting now...', err);
    process.exit();
});

// Require routes
require('./routes/department.routes.js')(app);
require('./routes/category.routes.js')(app);
require('./routes/product.routes.js')(app);
require('./routes/order.routes.js')(app);

app.listen(3500, () => {
    console.log("Server is listening on port 3500");
});

Here is a sample model:

const mongoose = require('mongoose');

const ProductSchema = mongoose.Schema({
	category_id: {
			type: [mongoose.Schema.Types.ObjectId],
			required: true
		},
	name: {
            type: String,
            required: true,
            unique: true
        },
	description: {
            type: String,
            required: true
        },
	price: {
            type: Number,
            required: true
        },
	discounted_price: {type: Number, default: 0.00},
	image: String,
	image_2: String,
	thumbnail: String,
	display: { type: Number, min: 0, max: 3, default: 0 }
});

module.exports = mongoose.model('Product', ProductSchema);

Here is a sample route:

module.exports = (app) => {
	const products = require('../controllers/product.controllers.js');

	// Create a new product
	app.post('/products', products.create);

	// Retrieve all products
	app.get('/products', products.findAll);

	// Retrieve a single product with productId
	app.get('/products/:productId', products.findOne);

	// Retrieve a products with categoryId
	app.get('/products/:categoryId', products.findWithCategoryId);

	// Update a product with productId
	app.put('/products/:productId', products.update);

	// Delete a produt with productId
	app.delete('/products/:productId', products.delete);
}

How do i also transfer my localhost database to Google Compute Engine

The easiest way is to use a database as a service (daas) from Mongo DB:
https://www.mongodb.com/cloud/atlas