I have created an auxiliary column. There I enter the following formula in the second row. This is filled in automatically for all following lines. The date is on the "C" column.
=ArrayFormula( IFERROR( if(C2:C<>0;(TEXT(day(C2:C);"00")&"."&text(month(C2:C);"00")&"."&YEAR(C2));"")))