How to use the bottender.MessengerHandler function in bottender

const { MessengerBot, MessengerHandler } = require('bottender');
const { createServer } = require('bottender/express');

const config = require('./bottender.config').messenger;

const bot = new MessengerBot({
  accessToken: config.accessToken,
  appSecret: config.appSecret,
});

const handler = new MessengerHandler()
  .onText(/yo/i, async context => {
    await context.sendText('Hi there!');
  })
  .onEvent(async context => {
    await context.sendText("I don't know what you say.");
  })
  .onError(async context => {
    await context.sendText('Something wrong happened.');
  });

bot.onEvent(handler);

const server = createServer(bot, { verifyToken: config.verifyToken });

server.listen(5000, () => {
  console.log('server is running on 5000 port...');

})
    .onText('\/help', async context => {
        await context.replyText(welcomeMessage)
    })
    .onText(async context => {
            const text = context.event.text
            const userId = context._session.user.id
            const reply = await olami.nli(text, userId)
            await context.reply([reply.toLineMessage()])
        }
    )
    .onError(async (context, err) => {
        await context.replyText('對不起唷~ 我需要多一點時間來處理 Q_Q')
    })

exports.messengerHandler = new MessengerHandler()
    .onText('\/help', async context => {
        await context.sendText(welcomeMessage)
    })
    .onText(async context => {
        const text = context.event.text
        const userId = context._session.user.id
        const reply = await olami.nli(text, userId)
        await context.sendMessage(reply.toMessengerMessage())
    })
    .onError(async (context, err) => {
        await context.sendText('對不起唷~ 我需要多一點時間來處理 Q_Q')
    })