Also, it seems you are using baked lighting so it would be better to add more lights to your scene in the darker areas if you want light there. Otherwise, the result you currently have is correct. Increasing the Ambient Lighting Intensity to make the darker parts look like they have light will only further mess up the lighting.
Another option is to add the Shadows, Midtones, and Highlights post effect to the volume and increase the shadows. This might help but ultimately the correct solution would be to use more lights.