Hi there, jamie-voss.
Undoing the previous bank reconciliations is only available in QuickBooks Online Accountant.
It's best to work this matter together with your accountant since they have an option to undo your previous reconciliation and help you start it over from the beginning. With that, I recommend inviting your accountant and let them undo the reconciliation period at once.
- Go to the Gear icon in the upper-right corner.
- Click Manage Users under Your Company.
- Select Accounting firms tab, and click the Invite button.
- Enter your accountant's email. Then, click the Invite button.
- Click Save.

Your accountant will receive an email. Inform them that they'll need to accept your invitation through email. Afterward, they can access your book and be able to help you undo the entire reconciliation. Aside from that, they can assist you further on the accounting side.
Let me know if you have other questions about reconciliation. I'll be around to assist you whenever you need help. Stay safe.