How to report Schedule D capital gain/loss as self-employment income on a Schedule C

I'm using Turbotax Home & Business, tax year 2024.  I have significant capital gains on my schedule D (from a brokerage 1099-B) and would like to transfer that to my Schedule C as self-employment income. 
The IRS says I can do that by adding that income to my Schedule C before adding it to line 12 of the 1040. 
However I can't figure out how to do that in Turbotax, which doesn't allow me to remove it from the 1040 line 12.
Please advise.  Thanks,