How do I change my Pennsylvania School District worksheet? It's stuck on Adams, and I need it to be Philadelphia. I don't know what form to delete in order to reset this

You will need to go back through the state return itself from the beginning to change this selection.

• Log into your account and click the State tab and click Continue next to Pennsylvania on the Status of your State Return page
• Click Continue and begin to go back to the questions
• You will get a few opening questions and then you should come to a page that asks What County you Lived in? - select Philadelphia
• For Philadelphia, there is only one school district so you should get the screen below (if you had chosen another county, you would get a drop-down list)

Note:  Try the above first, but if something is stuck on Adams and it won't let you change it.  Go to Tax Tools on the left-hand side of your screen and select Tools then select Delete a Form from the popup window.  Scroll to your PA forms and delete the PA School District Worksheet.  There is actually nothing on that form except for the name and code of the school district you live in, so deleting it should reset any selections.  You would then need to go back and do the steps above to select Philadelphia.  

Not allowing me to complete taxes because school code is not correct. How do I change

If you’ve tried AnthonyC’s procedure, above, and it doesn’t work, your best bet may be to clear your state return and start it over.

Please see the TurboTax Help article “How do I delete my state return in TurboTax Online?” or "How do I clear my state return in the TurboTax for Windows software?" as appropriate for guidance.

Even after deleting the school district codes worksheet, there is still a glitch. There is nowhere for me to complete this form online after I delete the worksheet, and then during my state review before filing, it just tries to get me to fix it - with Adams County still being the only county that can be selected. I need it to be Allegheny. Even when I call customer support, they're unable to help.

Omgosh wrong  school district was selected in personal info of state return. 

We had to go back to update the personal info on the state return. In this area, you have to select the county and then select the correct school district. This was done on TurboTax mobile app.