Client requires a restart of her books, due to errors and duplications that came from transferring data from another software. Best method to accomplish this?

If your client's books are less than 60 days old, you can purge their data in QuickBooks Online to start fresh, Jeremy.

Using this method will allow you to reenter or transfer everything correctly, as it completely clears out their books. Otherwise, you'll have to cancel their existing account if their books are more than 60 days old and sign up for a new QuickBooks Online (QBO) account to start fresh.

For detailed instructions, please refer to the 'Start Over in QuickBooks Online' section of this article: Delete your data and start over in QuickBooks Online. For personalized steps, you can log in to your client's QBO account and refresh the article.

Feel free to ask us if you have more questions about restarting your client's books.

@Jeremy-Mosher 

Did they purchase a 3rd party service to convert data from another program to QBO?

Thank you for replying. 

No, they did not. Prior to them contracting me, they did it themselves, but were using another accounting program. Part of the issue is that they created some extra accounts (duplicated their bank account) which I have deactivated, but the main issue is there are a lot of "duplicate" entries that part are reconciled, and the other half is not. If you get what I am trying to say.

I can delete/remove these duplications, but it throws all the bank reconciliations out. 
Another issue was/is they had a lot of personal investment into the company (using personal funds to purchase supplies, etc) and those were never accounted for correctly.

Now I can go back year by year and make entries and adjustments... but I feel like it would be more beneficial just to start with a clean slate. So I am mainly wondering should I just reverse all the reconciliations, or should I do a complete "rebuild" so that things the owner and others missed are catagorized properly.