If you applied a setting change or effect to a clip in GoPro Studio, but do not see any change in the preview, there are a couple of likely reasons.
You may have accidentally applied the effect to a clip in the Media Bin instead of in the Storyboard. If this is the case the effect would not show when previewing your Storyboard.
If this is the problem, click on the correct clip in the Storyboard and then make any necessary changes.
The Split screen control may have been accidentally moved all the way to the right. This would mask any setting changes that were made to the clip.
If this is the problem, slide the Split screen control slider all the way to the left.