1. Open cut and add video.

2. Click "Zoom" to modify the size of the video. The video size ratio is 9: 16, so 9: 16 is selected.

3. Go back to the previous level, select the "background" option, then click "Canvas Style", and then click the second option to select a picture.

4. Finally, add the background, and click the upload option in the upper right corner to save it.