If using Desktop, click HERE
If using Mobile Web (not the app), click HERE
To 'zero out' your notification center without opening each notification....
1. Open the App
2. Click on the notification bell in the top right-hand corner.
3. Click "Read All".
4. You will notice that all the notifications turn white to indicate that all of your messages have been read.
Now that you know how to clear the notifications in your bell, head over to the site and give it a try by clicking HERE.