I understand the need to move your data from QuickBooks Online to Self-Employed, @Mark11_2. Let an overview and explain how you can transfer files to QuickBooks Self-Employed.
QuickBooks Online is a more comprehensive accounting software created for small businesses that have employees, vendors, and inventory. On the other hand, QuickBooks Self-Employed is a standalone product. It is designed for individuals who have a single industry and do not have employees or inventory items. That said, both subscriptions have different features, and there isn't a way to transfer data directly to both or vice versa. You'll want to cancel your QBO account and then, sign up for a new QBSE subscription.
The only way to transfer the data is by exporting from the Online version and importing it to the Self-employed version of QuickBooks. See to it to secure a local backup copy of your company before doing the process: