Hello, Stephanie1708.

I know it saves time just making corrections of all transactions by exporting and importing them in QuickBooks Online. You'll have the option to export your invoice and credit notes to Excel. However, importing them back is only applicable for invoices. You may consider looking for a third-party application to import your customer's credit note by going to the Apps menu.

Here's how:

1. Go to the Sales menu, then All Sales.
2. Click the Filter dropdown, then under Type select either Invoices or Credit notes.
3. Fill in the necessary information, then Apply.
4. After that, hit the Export To Excel icon.

Also, changing or restoring data from the previous period isn't possible. You have to change or delete each incorrect transaction one at a time. Additionally, you can remove the transaction first if you want to import the corrected ones to avoid duplication.

You may consider checking this article for more insights: Void or delete transactions in QuickBooks Online.

I've also included this resource for future reference in exporting data in QuickBooks Online: Export data, reports, lists, and more from QuickBooks Online.

If you have other questions about the import and export process, do let me know. I'll be here to help you.