There is no direct way to set or clear a flag.
This was a feature in the short-lived ActiveHome 2 (CM14). In AC2, one was able to have a flag status popup, and from within that, see the current state, plus set or reset any of the flags.
AH2 also allowed you to give a name to any of the flags. That made using them in conditional macros, much more intuitive.
Possibly, this feature could/should be added to AH Pro??? I would sure like to see it return.