If it is a windows form Datagrid, you could use the below code to format the datetime for a column
dataGrid.Columns[2].DefaultCellStyle.Format = "MM/dd/yyyy HH:mm:ss";
EDIT :
Apart from this, if you need the datetime in AM/PM format, you could use the below code
dataGrid.Columns[2].DefaultCellStyle.Format = "MM/dd/yyyy hh:mm:ss tt";