Can anyone help me with how can i modify volume for a VIDEO prop ? 

Separate the audio from the video.
Then do the following:-
1.  Click Create>Create Sound>SoundFX1
2.  Choose the audio.
3.  Click Track List>Project>SoundFX1 in the Timeline.
4.  Click SoundFX1 tab.
5.  The audio clip should be in the track.
6.  Click Animation>Sound Modifier>SoundFX1
7.  Modify the volume/ Fade in/ Fade out.


YouTube Tutorials Here

Both video and audio can be processed separately. If you want to adjust the audio volume separately, you need to separate the video and audio first. Open TunesKit AceMovi (the simple video editor I use), right-click to detach the audio after adding the video to the timeline, so you can adjust the audio volume in the upper right corner of the interface.

I totally agree with hyinghui41. You can edit separately the audio and video in a simple video editor. I personally use movavi when I need to edit something, whether it's a slow-mo video, a slideshow, a video for Youtube/Instagram, and so so on. Whatever you choose and need just try https://www.movavi.com/videoeditor/.