First of all, I'm assuming that this is foreign tax reported on a 1099 and your client is not eligible for §904(j) election.

You can enter -01/01/01 (yes, a negative date) to print "Various".  However, that is not acceptable for MeF which, of course, is not an issue if you're client is planning to paper-file.  To avoid a critical diagnostic and enable e-filing, you can simply enter 12/31/2020.