Hello, is there any way I can combine all historical data from two companies (separate accounts) under one account?

You should signup for a new blank QBO Plus account. You may need to utilize the class tracking and/or location feature later to separate transactions.

https://quickbooks.grsm.io/EU

then you may have 2 ways:

1. Utilize a migration tool

https://get.transactionpro.com/qbo

2. Purchase a 3rd party merging service

Yes, there is, s-riyami7. 

I'd be delighted to share some information about combining your QuickBooks Online (QBO) historical data into a single company account.

We can start by manually exporting your QBO historical data to make a copy of your company's data and download it to your local hard drive. Here's how you can export your reports or lists:

1. Select the Gear icon from the toolbar.
2. Under Tools, choose Export Data.
3. Set the date range on the Reports tab.
4. Add or remove items from the Reports and Lists tabs by toggling the slider.
5. Once done, tap Export to Excel.

To export your non-posting transactions and attachments, please refer to this article for more details: Export data, reports, lists, and more from QuickBooks Online.

After exporting the data, you can now import the data into your single company. Please refer to this article for more information about the importing data process: Common questions about importing data to QuickBooks Online.

On the other hand, you'll want to utilize what Fiat Lux-ASIA has shared above or look for a third-party app that lets you migrate or merge your data automatically with a single QBO company.

Please don't hesitate to reply to this thread if you have any other questions regarding combining your QBO company data. I'll be here to answer them for you. Keep safe!