Due to retroactive law changes, the 'default' is that the 2019 NOL is carried BACK 5 years.  As was mentioned, it is too late to file a 1045, so amending those prior years with a 1040X is how you would claim the carryback.

However, if the 2020 tax return has been extended, you still have the option to "waive the carryback" for the 2019 NOL, in which case it would be carried to the 2020 tax return.