Newbie question: how to replace non-date with date when Find box won't allow a non-date entry?

Hi!  I'm importing approximately 100 "Line Lists" of people with COVID19 in congregate care facilities (Nursing Homes, et.) per day.  Each list has a lot of other data to be cleaned as well - demographic and symptoms.  I am getting overwhelmed by the number of tables and the number of typos in each.  Doing some of the cleanup systematically in Power Query would be a huge help.

Thank you very much for your help!