What screen are you seeing that in?  

Lacerte does the math automatically if all insurance & W-2 info is linked correctly.

Indiv Return, Screen 20 'S Corp', Line 17 'Other Info', SE Health Insur Premiums $6000, check mark next to 'Reduce QBI by SE health Insurance', nothing happens - (on my QBI business income calculation it does not reduce by $6000 for SE Health Insurance)

On my 2018 Lacerte it DOES reduce qbi by health Insurance, by following above steps

On my 2019 Lacerte it does NOT reduce

thank you

I've never used that....learned some new.  I use screen 24 & link it.