Mine didn't show on the app...I had to log on the desktop website and click my itinerary to add your dining choices...I read that somewhere in this thread and it worked!
THIS.
I actually brought up both the Be Our Guest page (no success) AND the my itinerary (THAT WORKS!)
Do this, and you SHOULD be able to work it.
In addition, it found available times - and I was able to refresh if necessary.
Good luck!