Adding payroll to your QuickBooks Self-Employed (QBSE) account is currently unavailable. This is because QBSE follows the Schedule C categories the IRS has for self-employed individuals.
What you can do though is to choose the closest category available for your payroll transactions:
If you decide to purchase to track payroll, you will need to cancel your QuickBooks Self-Employed account and sign up for a new account for QuickBooks Online.
To get a backup of your transactions from QuickBooks Self-Employed, you can download all your transactions from the Transactions page. For more detailed steps on switching to QuickBooks Online, check out this helpful article: Switch to another version of QuickBooks from QuickBooks Self-Employed.
Let me know if you have any other questions! Take care.