Hi webmasterlein
You can override the date format by going to Backend >> Extensions >> Language(s) >> Overrides
Select language on your site (German I guess) >> add New override for this language constant: TPL_DATE_FORMAT_LC1
pls note that in above screenshot, I test for English, you need to select your own language.
And I'm not sure which format you want so you can change the value: d. m Y to your desired value. More info here: https://www.php.net/manual/en/datetime.formats.date.php