Adjust the volume for a selection of a video?

[kellogs]

I have an .mp4 video where for 4 seconds someone screams very loudly, and I'd like to adjust the audio to lower it for those few seconds. However, I am not entirely aware how to do this. Additionally, Avidemux has made it difficult for me to pinpoint the exact time selection I'd like to adjust (using the A and B selection skips back and forward and not to the exact time I want). Perhaps there is a simple way I am not aware of?

thanks in advance 

[WellTell]

I would use some audio editor for the audio track, such as Audacity. Then encode audio and video track via Avidemux.