Can I un-decline a game and change my response to "accepted" ?

Unfortunately, not directly. Once a game is declined it is immediately removed from your schedule and sent back to the scheduler for rescheduling. Officials would need to contact their scheduler if the decline was inadvertent and the scheduler can reschedule the game back to the original official.

For Schedulers:
When an official declines a game, they will be forever marked "Unavailable" for that game. If you want to reschedule them to that game, you would need to assign them from the "Unavailable" list which is no different from assigning regularly, you're just going to need to view and use the list of "Unavailable" officials instead of the "Available" officials.

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