If you'd like to create a Vertical Video from a video, select the Publishing Tools icon from the left rail and select Video Studio. Then, select "Upload media." You can either upload a file from your computer, or input the media URL.
Once the video is loaded, you can make adjustments. Click on the "Background" menu at the top and select "Color" to change the background color, "Opacity" to change the opacity of the background color, "Upload Media" to choose a new one to replace the existing or "Reset" to remove the applied filters.