TP had a $35K NOL for 2018 on Sch. C.  No tax was due.  New Covid rules say we can now carry back 5 years starting with 2018 NOLs. 

In 2016 TP had wages of $67K with tax Liability of $7,289.  No Schedule C income or SE tax.   

In 2017 TP had $35K Sch.C income and 7K Wages.  Income Tax liability was $4K and SE Tax was $5K.

Do I start with tax year 2016 or 2017?  It will get used up either way.  Seems to have more value in 2016 since NOLs cannot offset SE Tax.