Click on the clock icon in the main menu and then on Reminder.
The number in the red circle shows the number of expired or expiring reminders; if there are none, no number appears.
By default, the list opens sorted by the Reminder date field, filtered to see only those expired or expiring in the next 24 hours.
The reminder date is colored red if it is past, in orange if it is coming and in black otherwise.
Remove the expiration filter by choosing Show all in the options at the top, or putting it back by selecting expired and expiring in the next 24 hours (default option).
Click on the red bell at the end of every row to remove the notification for that reminder.
Pay attention, in this way the notification will not reappear, click to remove it only when you are sure.