Within the selected video template, click on the gray background labeled "Video" or "Image or Video." This section always features a film strip icon.
If you don't see this, it means you cannot add a video to your slide.
This action will open your file browser, allowing you to select the desired video. Once you've selected a video, a window will appear, enabling you to edit it.
After editing, click the "X" in the top-right corner of the window to close it.
Congratulations ! Your video is now integrated into the template.