to calculate your 2020 NOL use form 1045 Schedule A. if you did not make an election to carry it forward on the 2020 timely filed return it must be carried back to 2015 which Turbotax no longer supports
https://www.irs.gov/pub/irs-pdf/f1045.pdf form
https://www.irs.gov/pub/irs-pdf/i1045.pdf instructions
