Can I continue to contribute to a SEP IRA if I'm over 70-1/2 and still working as a self-employed individual?

Contributions to a SEP IRA can be very flexible. If you have earned income after the age of 70 1/2, you are still allowed to contribute.

Specifically, net profit from self-employment.

tell me how to do that with your software

Taxpayer is over 70 1/2 at end of 2019. Taxpayer took a Required Minimum Distribution in 2019. Turbo Tax is allowing taxpayer to take a deductible contribution even though a contribution to a traditional IRA would not be deductible.

Correct since the contribution you are referring to, indicated in your separate question elsewhere, is a SEP contribution.  Permissible self-employed SEP contributions are always deducted.