Make a section of song lower for 30 seconds, then bring it back up again

I have a song on A2 and a Video on V1 and its Audio on A1. The song starts to play at normal volume but I want to lower the volume about 30 seconds in so I can hear the real audio on A1. Then after 10 seconds of that, I want to raise the volume of the song again.

I know I can make a cut in the song using the Razor Blade Tool at the points where I want the song to be lower.

How can I make that piece lower and not the entire song?

Thanks in advance