Hi, I have a QuickBooks account since June 2020, I use the it for self employed company, also I own a Limited company, how can use the same app to manage my new company?

Welcome to the Community, jcharrow66-gmail.

You'll need to have a separate QuickBooks Self-Employed account for each company. For a second company, you can sign up for a new QBSE account. Take note that you can use a different email for the new subscription.

In addition, every QuickBooks account is charged. You can refer to this guide to manage your subscriptions: Update your billing and subscription info in QuickBooks Self-Employed.

Feel free to visit this resource to learn more about the QuickBooks app: The QuickBooks App—take your business with you. This helps you manage your business on the go.

I'll be right here to help if you have further questions about managing your account. Have a great day!

@jcharrow66-gmail 

One QBSE/QBO account is for one company file. You may manage branches/divisions by utilizing the Class/Location feature available in QBO Plus. Otherwise you should open a new account.

https://quickbooks.grsm.io/UK