Deploying Nodejs Express js App on heroku

I’m trying to deploy my app on heroku, but I’m always getting this error

2022-08-11T12:49:12.131468+00:00 app[web.1]: Error: connect ECONNREFUSED 127.0.0.1:3306
2022-08-11T12:49:12.131469+00:00 app[web.1]: at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1247:16) {
2022-08-11T12:49:12.131470+00:00 app[web.1]: errno: -111,
2022-08-11T12:49:12.131470+00:00 app[web.1]: code: 'ECONNREFUSED',
2022-08-11T12:49:12.131470+00:00 app[web.1]: syscall: 'connect',
2022-08-11T12:49:12.131471+00:00 app[web.1]: address: '127.0.0.1',
2022-08-11T12:49:12.131471+00:00 app[web.1]: port: 3306,
2022-08-11T12:49:12.131471+00:00 app[web.1]: fatal: true
2022-08-11T12:49:12.131472+00:00 app[web.1]: }
2022-08-11T12:49:12.131494+00:00 app[web.1]:
2022-08-11T12:49:12.131494+00:00 app[web.1]: Node.js v18.7.0

Could anybody help me solve this problem?
This is the server.js

const express = require('express')
const app = express()

app.set('view engine', 'ejs')

const filterByDateRouter = require('./routes/filterByDate');
const filterByLogsRouter = require('./routes/filterByLogs');
const mainPageRouter = require('./routes/index'); 

app.use("/filterByDate", filterByDateRouter)
app.use("/filterByLogs", filterByLogsRouter)
app.use("/",mainPageRouter)
app.use(express.static(__dirname + '/public/css'))
app.use(express.static(__dirname + '/public/js'))


app.listen(process.env.PORT || 3000)

this is the database connection:

var connection = mysql.createPool({
  host: process.env.DB_HOST,
  user: process.env.DB_USER,
  password: process.env.DB_PASSWORD,
  connectionLimit:10,
  database: process.env.DB_NAME,
});

I’m using clearMYSQL from heroku to deploy my database, and all the fields saved in the .env are right