How do I file a PA-40 form if I've already filed my return? I was unaware of this form and I don't work in PA at all, but I pay PA state income taxes.

Yes. If you are a nonresident of Pennsylvania, but Pennsylvania state income tax was withheld on your wages, you will need to file an amendment to get a refund of your tax paid. Per the State of Pennsylvania, if a PA-40 Nonresident Consolidated (NRC) Income Tax Return is filed, the overpayment will be refunded.

If your e-file is still pending, you won't be able to make changes until your return is either accepted or rejected. 

Once your returns are accepted, please follow the directions on the How do I amend my 2020 return?

After your amendment is started, you need to add a nonresident return. 

Please follow these steps in TurboTax:

1. Open your return. 
2. Click on State on the left-hand side.
3. Add Pennsylvania. 
4. Follow the on-screen instructions.