When a date has an invalid date '0000:00:00 00:00' and you would like to have (NULL) values in it, you can do the following in f.e. Heidisql:
update your_table yt set yt.wrong_date = NULL WHERE CAST(yt.wrong_date AS CHAR(20)) = '0000-00-00 00:00:00'
Make sure that the date field accepts (NULL) values
Don't do this with Mariadb, it is not supported