When I go to reconcile my account for 2020 months, transactions from 2019 keep appearing. How can I clear them?

Hi there, @onesweetwriter.  

Welcome to the Community. Deleting the previous year's unclear transactions may cause serious complications, and could mess up with your reports. 

Instead, you create a journal entry to reverse the transaction so it will remove for this year's reconciliation. Here's how: 

1. Click the + New menu, then select Journal entry. 
2. Enter all necessary information in the fields to create your journal entry.
3. Select Save and close.

I'd also recommend seeking advice from your accountant on how to correct the prior year transaction accounting.

Just in case, I've added an article for your reference about the reconciliation process in QuickBooks Online: Learn the reconcile workflow in QuickBooks. It also includes links to different topics that will guide you on what to do in case you'll encounter any of the scenarios listed.  

Let me know in the comment below if you have more questions. We're always delighted to help you more.