I was suppose to amend my 2018 tax return because I neglected to add info from my TC-20S. Should I amend my 2018 return before doing my 2019 return??

It is best to Amend your 2018 tax return first because numbers may affect your 2019 return. Please see the TurboTax FAQ below for instructions:

How do I amend a 2018 return in TurboTax?

Thanks.  No lets hope I can figure out what to do with my TC-20S and Sch. K-1.