Delta only offers Standby for Gold Medallions or above (unless you have been affected by IROPS). The same day confirmed travel change option is not available for international flights (except Canada and some US territories).
You can use the same-day confirmed option for travel within the United States, Canada, Puerto Rico, and the U.S. Virgin Islands on Delta and Delta Connection® flights.
https://www.delta.com/traveling_chec...nges/index.jsp