if you did not include in your 2018 return an election to carryforwrd your 2018 NOL on your timely filed '18 return, you must first carryback the loss to 2016 and then carryforward any remaining loss to 2017. after that any remaining loss gets carried forward to 2019. any net loss on schedule C and any other ordinary losses elsewhere on the return (except net capital losses) become part of an NOL calculation. an NOL is not reported on Schedule C, it is reported on schedule 1 line 8 for 2019
there is a form 1045 schedule A which can be used to calculate your NOL on page 3
https://www.irs.gov/pub/irs-pdf/f1045.pdf
