To find the Self-Employed Health Insurance deduction, go to Business->Business Income and Expenses.
When you create or edit a business, go to Business Expenses->Other Common Business Expenses. Under that will be an entry labeled "Insurance Payments". Click on that and you can edit the amount of your health insurance premiums under "Health Insurance Premiums".
This result will carry automatically to line 16 on Schedule 1 (1040).
[Edited 4/2/2020 1:29 pm CDT - updated for 2019]
