Help changing: DD-MM-YYYY HH:MM to YYYY-MM-DD HH:MM

Hi,

I am struggling with changing date formate in Excel form DD-MM-YYYY HH:MM to YYYY-MM-DD HH:MM 

I have tired to custom change with formate but it does not work.

I looked online and found few function like Isnumber or Iftext but it never worked. 

I need your help please as I am trying to export my excel data to WEKA which only recognize this formate YYYY-MM-DD HH:MM

There is also another problem. Even if I right the date I want from scratch the cell value at the top bar shows seconds and AM/PM. Changing cell formate does not change anything.

Thank you very much in advance!