Easiest method is use the Change Reservation feature on the app/web site.
I just did it several times on our trip.
It has always worked for me as long as you are within about 2 hours of the meal
I change the time to whenever I can find a time, as long as it's in the future.
Once I change it, I cancel the ADR.
The only time that didn't work was for a Dining Package, like Jungle Book or F!