Amending a PA non-resident return for NJ resident
I'm trying to help my son's friend. He filed his Federal return and a PA non-resident return using TurboTax on his phone. He is a NJ resident working for a PA company, and did not know to mark the wage income as non-taxable in PA. (I'm a little surprised TT didn't flag that for him.) I've seen on other posts instruction for indicating this income is not taxable to him in PA in his profile, but we are unable to locate/access that function on amending his return. Unfortunately, he was given incorrect information regarding the tax reciprocity agreement, and has yet to file his NJ return. He says he has tried several times, but has not been able to file the NJ return with TT. I've used TT for over 25 years, this just doesn't sound right to me.
Questions:
1) Is there a way to file an amendment in TT on the non-resident PA return where he reflects his wages as not subject to tax, since he overlooked that step in his initial filing? If so, how/where would he indicate that?
2) Is there any reason TT will not allow him to file his NJ return, albeit late?
3) Would it be advisable to handle the PA amendment and the NJ filing on a PC, or is the functionality the same between PC access and mobile access?
Thanks for any guidance and assistance!