It seems that the option to edit Google Assistant reminders currently isn’t working for many users around the world.
Although you can still create new reminders via voice, manual editing appears to be broken for many Android users, as first reported by Android Police.
The problems seems to be that when users ask Assistant to display their reminders and then tap on an individual reminder to edit it, a loading animation pops up and the assistant will tell you “I don’t know which one you meant, I sent a notification to your phone so you can choose which reminder to update.”
If you try to edit the reminder through the notification, the process repeats itself again preventing you from actually being able to edit it.
It’s unknown what’s causing the problem, but there are other ways to edit reminders. For instance, you can edit the title and time on Google Calendar, or you can ask Google Assistant to edit it directly if you remember what you specifically named the reminders.
Source: Android Police