I see there is not much of an activity here. however I did got response from the support team:
"unfortunately notone fast way to do this is to split the audio clip where the video clips start and finishthen just mute or delete the audio clip"
and this was my response:
Thanks for your response
I must admit that I am a bit disappointed
It is very common to have video clips integrated inside your slideshow and reducing the volume of the background music is a must.
The manual way of doing so takes so much time, which causes the overall time you spent on the slideshow to be much longer.
Also when you do in manually, after you adjust the volume along the timeline you are limited to add changes to your slideshow cause once you change something in timeline you need to rework the volume adjustments
I have some programming background and I believe it is relatively not too much effort to implement such a feature.
I highly suggest that you consider adding this feature