You may change the video duration time in several ways:
👉via the additional toolbar. Press on the added video to see an additional timeline. There you should press on the «Scissors» button, and you would be able to change your video duration.
👉via the Timeline. Open the Timeline by pressing on the «Pencil» button and choosing the «Timer» section. Change the duration of the project by swiping the «Total» line to the right (to expand the duration) or left (to shorten the duration).