I have an assistant with an ID created from the platform.openai.com. I want to use it instead of the default gpt. How do I do that?

import { config } from "dotenv";
config();
import { OpenAI } from "openai";
import readline from "readline";

const openai = new OpenAI({ apiKey: process.env.API_KEY });

const userInterface = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
});

let messages = [];

userInterface.prompt();
userInterface.on("line", async (input) => {
  messages.push({ role: "user", content: input });

  const res = await openai.chat.completions.create({
    model: "gpt-3.5-turbo",
    messages: contextMessages,
  });
  const assistantMessage = res.choices[0].message.content;
  console.log(assistantMessage);
  messages.push({ role: "assistant", content: assistantMessage });
  userInterface.prompt();
});

I can fetch the assistant through the api by creating a thread and a run like below. I just dont know how to use it in the code above, so the user is chatting with my custom gpt assistant.

const emptyThread = await openai.beta.threads.create();

const run = await openai.beta.threads.runs.create(emptyThread.id, {
  assistant_id: "asst_DmX0pcXXXXXXXXXXX",
});

console.log(run);