field management - value of date

Dear all,
Could someone tell me what the default value is of the field 'Date'? How can I change the default value? Further, the date field becomes empty after I downloaded a user record as a CSV file, changed the date value within Excel and uploaded the CSV file. I do something wrong ...

Thanks in advance,
Hans

Import/Export works only with database stored values. So if you're adding a date to a date field it needs to be in the 0000-00-00 format. For example today would be 2020-08-14. For datetime fields it's 0000-00-00 00:00:00. Note stored datetime values should always be in UTC as they're offset on display.

Fields typically do not have database stored default values beyond empty and those can not be changed unless you modify the database. If you want to change the default value of a field during registration you can do so using the "Default Registration Value" parameter and that parameter again works with database stored values (so for a date field see my above explanation and examples).