I always have a hard time trying to add or minus days to a given date in Datastage. You can use icon, ocon too....but I like this method when I need to manipulate a date column in Transformer Stage.
To add one day to a given date (an incoming date column):
DateFromJulianDay(JulianDayFromDate(DSLink1.your_date_column) + 1)
So basically you convert a date to a julian day, then add 1, then convert the julian day back to a date.