Hello. Could you tell me please, how can I use several of my companies under one account in quick books? Unfortunately I can't find this option.

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

https:// quickbooks.grsm.io/US

https:// quickbooks.grsm.io/us-promo

You may also consider having an additional app to consolidate reports from multi QBO accounts.