In QuickBooks Online, the Employer Settings option is visible when you click the Cogwheel ⚙️ icon found in the upper-right corner. As long as you have the right region, you'll be able to turn on the option from your account.
Click the Cogwheel ⚙️ icon in the upper-right corner.
Under Your Company, select Employer Settings.
Go to the Employer Details tab.
Tick the Employment Allowance Enabled box.
For additional information, I've attached an article about turning on employment allowance and how to submit an EPS to HMRC: Employment Allowance.
I'm only a few clicks away if you have any other questions. Wishing you and your business continued success.