Hello, JWolf1.

Closing of books is an important feature in QuickBooks that protects against accidental changes that affect your financial reports. You'll need a pin or password to change the email on the invoice.

Just to make sure, are you login as the primary or company admin? If yes, you can re-open the closed period by clearing the closing date. You can then unlock the book by providing a new password and confirming it.

Here's how:

1. Sign in to QuickBooks Online as a primary admin or company admin. 
2. Go to Settings ⚙ and then select Accounts and Settings.
3. Select the Advanced tab.
4. Click Edit ✎ in the Accounting section.
5. Delete the date and uncheck the box. Note: To change your password, just enter a new password and confirm it.
6. Select Save and then Done.

Once done, you can open the overdue invoice and update the email address.

Please visit this link for further details about editing a closed books: Edit your closed books.

You can also review this article about recording payment for future reference: Record invoice payments in QuickBooks Online.

I'm just a post away if you need anything else. Have a great day.