Tap the Account tab then make sure you tap the Shared tab at the top of the screen (opposite Settings).
Swipe from right to left on the item you want to clear.
Tap the Delete button that appears on the left hand side of the item.
To re-share the video, first tap the Video tab.
Tap the thumbnail of the video you wish to share, then tap the Share button from the Action Popup Menu.
Choose you share destination and then tap the Send button.