First, file PA Form REV-419 with your employer to have them cease withholding for PA. Here's a link to that form:
https://www.revenue.pa.gov/FormsandPublications/FormsforBusinesses/EmployerWithholding/Documents/rev...
In order to obtain a refund of the incorrectly withheld PA taxes, you'll have to file a non-resident PA tax return, on which you show the withholding but allocate zero income to PA.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
