Okay, after days of searching, I give up, I'm just going to break down and ask.
So, the default Alarm Widget on the phone ("Tap to create alarm.") Once you've got that set to a certain time, it originally seemed to me the only way to "change" it was to delete the widget, make a new one, and set an alarm to the new one. But somehow, and I could not replicate this, I managed to change one of my alarms. I noticed because changing the time on one widget changed the another; somehow they had both become set to the same alarm, even though both of them had already been set. So there must be a way to change the alarm without deleting the widget first, but I can't find how on Google and no manual I've seen describes how either.
So, the default Alarm Widget on the phone ("Tap to create alarm.") Once you've got that set to a certain time, it originally seemed to me the only way to "change" it was to delete the widget, make a new one, and set an alarm to the new one. But somehow, and I could not replicate this, I managed to change one of my alarms. I noticed because changing the time on one widget changed the another; somehow they had both become set to the same alarm, even though both of them had already been set. So there must be a way to change the alarm without deleting the widget first, but I can't find how on Google and no manual I've seen describes how either.