Here is a video showing how to use Dubb’s built-in video editing features to trim out the parts of the video that you don't want to be included:
Here is how you can undo a trim that you performed on Dubb
Dashboard > Select Video > Then click on the editing tab:
Select the parts of the video that you'd like to trim out by using the timeline. For example, if you want to trim out the very beginning of your video. Just bring your cursor to the beginning of the video and then click set, then allow the video to play until the point that you want to trim it out. Then click set to select the end-point.
Then, click the + sign to add a new portion that you want to trim out. For example, you could also trim out the middle or end of your video.