For example if you want to set the alignment of the second column, here is the code :
var eApp = new Excel.Application { DisplayAlerts = false };
eApp.Workbooks.Open(@"c:\target.xlsx");
eApp.Visible = true;
Worksheet ws = eApp.ActiveSheet;
ws.Columns[2].HorizontalAlignment = XlHAlign.xlHAlignRight;
Hope it helps.