Is there a way to password-protect last year's books so no one changes anything by mistake?

Welcome to the Community space, @carolynjtaylor. I'd be glad to help you with the steps to protect your books from making changes in QuickBooks.

Yes, there's a way to password-protect your last year's books so no one can change the transactions by mistake. You'll have to select Allow changes after viewing a warning and entering a password option, so it will require a password before editing your books.

Here's how:

1. Go to the Gear icon, then choose Accounts and Settings. 
2. Select Advanced, then click the Edit icon perpendicular to Accounting. 
3. Pick Close the books checkbox, then enter a closing date. 
4. Select the Allow changes after viewing a warning and entering a password option from the drop-down menu to add a password. 
5. Tap Save and close. 

For more details, open this article: Close your books in QuickBooks Online. If you need to edit your books in the future, you may click this link: Edit your closed books.

Also, I'll be sharing these links on how to prepare your books and run basic reports in QuickBooks:

• Year-end guide and checklist for QuickBooks Online
• Run reports in QuickBooks Online

Let me know if there’s anything else you need help with in QuickBooks. I’d be more than happy to assist you. Take care.