Unfortunately, at the moment it's not possible to remove or move multiple sections of a video. Only the beginning and end of a video can be clipped.
We know that "multicrop" is something that would be very useful, but our goal is to keep Edpuzzle as easy to use as possible, and this feature is quite complicated.
For a temporary workaround, create multiple assignments from the same video and assign them individually. Your students will thank you for the shorter videos!