Adding another company to your Intuit profile or account is somewhat similar to setting up your first QBO company. I'll guide you through the process, and I'll add screenshots for your visual reference as well.
To do this, simply go to the Sign-in page and choose Create an account or Sign up.
On the next page, select a plan (or click Buy now or Start a trial first) because this will be an additional subscription under your profile. When you reach the Sign-up page, click on Add another company or add another company to existing login. Then, follow the on-screen instructions to finish your setup.
The next time you sign in, you will see the list of companies under your account, and you can open the one where you want to work on. When you need to switch to the other company, simply click the Gear icon and choose Switch company.
Feel free to check some of our help articles should you need them in the future. If you have questions, please don't hesitate to go back to this thread. Have a good day!