Hi keystone,
There are a few things you can try.
1. If there is a very clear point at which the audio becomes too loud then I would try selecting only the quiet audio and amplifying it using "Effects -> Amplify"
2. Try looking at "Effects -> Dynamic Range Compressor". This tool allows you to control how much attenuation or boost is applied to a section of audio based on how loud it is. So, in your example, you could boost are boosted and how much loud sections are reduced in volume. This can take a bit of playing around to get it right, but it can also do a very good job.
3. There is also "Effects->Normalize" which you may want to try applying to only the quiet section.
If you need additional help understanding the parameters for these tools, then let us know.
Regards,
Ben