yes, you can amend but any loss for 2016 and 2017 that would have been utilized is lost. 2016 and 2017 are closed years. any remaining can be used in 2018 but you only have until 4/18/2022 to file. any remaining can be used in 2019, then 2020, then 2021 any still used carries forward to 2022
you would need Turbotax desktop software 2018-2020 and would need to file by mail since e-filing for those years is closed.
