TurboTax says my earned income is $991, not $1,067, due to a $76 SE tax deduction. But that shouldn’t reduce Roth IRA limits. How do I fix or override this?

Sorry, For an IRA contribution.  If you only have self-employment income you can only contribute up to your net profit reduced by the deduction allowed for one-half of your self-employment taxes then only up to the max IRA limit.

See IRS publication 590 http://www.irs.gov/pub/irs-pdf/p590a.pdf

So check 1040 Schedule 1 line 15.  You have to deduct that amount from your Schedule C Net Profit.  That will give you the allowed contribution for self employment & 1099NEC income.