From the My Videos screen find the video you want to fix and tap the Gear icon.
Then tap the Edit button.
Tap Change Photo Cropping and Positioning.
Tap the photo for which you want to change cropping and/or positioning.
Then use two fingers to adjust your photo cropping, or one finger to adjust only positioning.
You can also turn photo movement on or off here by tapping the Photo Movement Icon.
To finalize your changes tap Save.
Once you're done making changes, tap Back, then tap Save.
Then tap Save again to give your video an updated title, then tap Save to let it process and upload.