Error TT414 migrated frm old to new computer,open 2018 return for updating-} "file created w ltr vers of TT than the 1 installed, must update to open file-but not avail??

An update for 2018 is unavailable, so how can the program be used (no updates are available before 2021 so you cannot edit any previous file you made (or did not file on time, for some people)