How do I lock past years in QB Self Employed version.

Glad to have you here in the Community, @fannypack.

Currently, we're unable to close past transactions in QuickBooks Self-Employed (QBSE). You can only download a PDF file of yearly reports.

If you need the Excel file for your past transactions, you may opt for a third-party conversion. You can search for some apps online on how to quickly export PDF documents into Excel files. 

QuickBooks Self-employed shares many features of QuickBooks Online, however, they are designed differently. You can learn more about this through this article: All Your Work, All in One Place: QuickBooks Self-Employed.

For more information, as well as how to download transactions in QuickBooks, I recommend the following article: Export transactions and get reports in QuickBooks Self-Employed.

Let me know if you have other questions or clarifications. I'm just around the corner if you need help. Take care and have a good one.