What is the easiest way to separate classes into different QBO files?

I'm not sure you can, but the better question to answer is why?

Classes are used to distinguish one activity from another, all within the same business.

If the client wants to start a new business in one of the class distinctions, that is what it is, a new business.  The transactions from the old business do not get transferred since they are used in the financials for the old business

@Mdaily1 

The easiest way is to purchase a 3rd party service to split the Class data into two or more separate QBO accounts. Otherwise, utilize a migration tool.

https://transactionpro.grsm.io/qbo

Our client has multiple tax EINs in the same file.  She does have them classed but really needs them in separate books for tax purposes.  

Essentially, there does not seem to be an easy way.  Export and import all I can and delete what is moved to the new company is all I am really getting...  Do you agree?

Thanks for visiting the QuickBooks Support page, @Mdaily1.

Allow me to share some information on how you can separate transactions for each departments or businesses in one QBO account. 

Yes, you can do that option if you have a separate company files to track the transactions for. Then, you may find a third-party deleter app to remove the data inside QuickBooks. Click this link to our site: QuickBooks Online Applications

Also, aside from classes, you can also tag transactions by departments using the Location tracking feature. This way, you're able to identify the transactions easily just by looking at the reports. These are the steps to enable the feature:

1. Tap the Gear icon and choose Account and Settings.
2. Go to the Advanced tab and pick Categories.
3. Use the Track Locations slider to turn on these features in your account. 
4. Select Save and then Done.
   

Once set up, you can assign these class  or locations your sales or expense transactions. See this example:

Once you have the transactions tagged, you can open any reports and filter by Class or Location. To learn more about how this features work and how to use them, check out these links:

• Set up class tracking.
• Set up and use location tracking.
• Video tutorials for QuickBooks Online.

Drop by the community for follow-up questions about this topic or if you need other things with QuickBooks. I'll be right here to help. Have a lovely week!