The vast majority of my Pennsylvania clients live in the suburbs of Philadelphia.  Keystone Collection is normally who collects the earned income tax.  Here is their website which will provide a great amount of information for you:  Keystone Collections Group (keystonecollects.com

The website will provide specifics on individual townships that impose an EIT along with the addresses you will need to file the form.  The address depends on the tax situation...do you owe, refund, no tax due.  There is a different address for each circumstance. 

It's important to know, not every town in Pennsylvania imposes an EIT, so make sure you investigate if the returns you are working on have that exposure or not.  

I use the form that Intuit provides, I check the box, print it, and add the respective W2's.  I sign the form, have my clients sign and then mail it in.  You'll need to determine if there is a refund, amount due, or if it's paid in full.  The program does a nice job of populating the pertinent information but you have to make sure you populate the appropriate tax the town imposes in order for the calculations to be correct.