If you haven't filed your PA return yet, then TurboTax will ask you this question during the interview process towards the end (look for the screen titled "Untaxed Out-of-State Purchases".
If you have filed already, then you have the option of either amending your PA tax return and including the use tax or you can file a use tax return directly online with PA using Online PA-1 Use Tax Return. (You will need to create an account for this purpose)
For more information, see -
https://www.revenue.pa.gov/GeneralTaxInformation/Tax%20Types%20and%20Information/SUT/UseTax/Pages/Us...
