I want to change my date (string) to a date format
%Y-%m-%d for the time manager. I already try with the Field Calculator. But it is not working. What should i write in the expression. And should I create a new field?
You should calculate a new field with field calculator. Notice the difference between capital and small characters! Here is an expression which should work. It first converts the content of your start_date field to a date type and then reformats it: