Greetings, @lee22.

Yes, you can delete all your online data and start from scratch. This feature is available to QuickBooks Online Plus or Essentials subscriptions. Let me guide you on how this works.

1. Log into your QBO account.
2. Change the URL to include /purgecompany.
3. Confirm you want to delete your company data, type Yes.
4. Click OK.
5. Choose Wipe Data.

You can do this for accounts that are less than 60 days from the day it is created and is irreversible. However, for accounts that are more than 60 days, you'll have to cancel your current account and start a new one. You can check this article for more detailed instructions: Delete your data and start over in QuickBooks Online.

On the other hand, if you're referring to starting a clean slate in your account's register, you can undo the added or matched bank transactions.

Here's how:

1. Go to the Banking menu.
2. Choose the Banking tab.
3. Select the Reviewed tab.
4. Mark all the transactions you want to undo.
5. Click the Batch Action drop-down.
6. Pick Undo.

Once completed, you can now match and categorize your bank transactions.

You can always leave a post or a comment below if you have other questions about managing your QuickBooks transactions. I'm just a few clicks away.